Catalyst characterization - American Chemical Society

Anal. Chem. 1987, 59, 68R-102R

Catalyst Characterization Robin L. Austermann, David R. Denley, Donald W.H a r t , Paul B. Himelfarb, Richard M. Irwin, Mysore Narayana, Robert Szentirmay, Sunny C . Tang,* a n d Randall C . Yeates Westhollow Research Center, Shell Development Company, Houston. Texas 77001

This is the inaugural review on Catalyst Characterization. The analytical characterization of catalysts, heterogeneous and homogeneous, occupies a central position in catalysis research, in academia, and in industry. The emphasis in recent years has been to attempt to gain a detailed structural picture of the catalysts themselves and then, by utilizing this information, develop better understanding as to the function of the catalysts and, hopefully, provide guidance in synthesizing new and improved catalysts. This review covers the journal literature for the period July 1984 through June 1986. The purpose of this review is to provide a summary of the major highlights in catalyst characterization during the review period and is not intended to be a comprehensive citation of the many articles related to this broad topic. As is befitting today’s environment, the first pass in searching the literature was conducted by computer, and it uncovered greater than 4000 references relevant to the characterization of catalysts. The nine authors, all chemists or physicists with the Analytical Department of Shell Development Company, were asked to critically review the citations within their fields of expertise, and the products of their efforts were then combined. In this review, the temperature-programmed techniques, such as temperature-programmed desorption and reduction, are separately treated in the sections Surface Analysis, Thermal Analysis, and Sorption Techniques. The acidity of a catalyst is an important parameter to determine from both activity and selectivity standpoints. Thus, this topic is treated specifically in several sections of this review: Nuclear Magnetic Resonance, Optical Spectroscopy, and Sorption Techniques. The approach of characterizing a particular catalyst by utilizing multiple analytical techniques is now widely used, and a section titled Multiple Techniques is included to review those papers in which four or more analytical techniques were used by the author(s).

X-RAY A B S O R P T I O N S P E C T R O S C O P Y For the period under review, greatest activity was shown in the areas of metal sulfide catalysts for hydrogenation, hydrodesulfurization, and hydrodenitrification and platinum or platinum-based bimetallic catalysts for hydrogenation and reforming. The remaining studies are spread fairly uniformly among a wide variety of catalytic systems. Extended X-ray absorption fine structure (EXAFS) has been applied to hydrodesulfurization mainly in the case of the Co-Mo/alumina catalysts. Oxide preparations for the catalyst have been analyzed with novel successive approximation techniques to show that apparent Mo coordination decreases as Mo loading increases (AI). Distortion of octahedral coordination of the Mo was inferred from the edge structure, and this was found to parallel the measurements of Mo coordination number. Cobalt addition was found to decrease the distortion. By amplitude analysis and comparison with other techniques, values for crystallite size and Co dispersion on MoSz edges have been reported (A2) and allowed the workers to conclude that crystallite size increases with an increase in either Mo loading or sulfiding temperature. A comparison of these systems with their activity values showed that both a high coverage of MoSz edges with Co and a high edge dispersion of Co were necessary conditions to higher activity (A3). Data have also been collected for several different programs of sulfiding (A4). In that study, kinetics of sulfiding were measured via X-ray absorption near-edge structure (XANES) features, values for the activation ener y and preexponential factor were obtained, and it was notecf that sulfidization was never found to proceed to completion. Incomplete sulfiding was also found to hold for W and Ni-W/SiOz catalysts (A5). While in situ sulfiding of these systems are common, work has begun to appear where the catalyst is measured in the course of reaction a t elevated pressure. The observation of one such study was that Mo-S 68 R

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and Mo-Mo coordination numbers were maximized a t the same promoter concentration that corresponded to maximum activity (A6). Measurements for Ni-Mo/alumina were able to identify Mo-Ni species, NiO, and NiAlz04( A n , although poor agreement with published reference spectra is to be found in the latter material (A8). The family of supported Pt catalysts is important commercially, and interest among researchers is high, but analysis of these systems has been retarded due to the complexity of these systems. Because of the high dispersion, particle size effects are important, disorder is high in most systems, and, in addition, the EXAFS phase shift is highly nonlinear for Pt. Nonetheless, careful analysis of the data has yielded information for a number of preparative states. The structure of a European catalyst standard EUROPT-1 (Pt/silica) was reported to be a disordered oxide (A9) when reduced at 473 K. In another Pt/silica system, Pt-0 binding to the support was reported with R = 1.91 8, and chemisorbed Pt-0 at R = 2.03 A (AIO). Temperature dependencies were ascribed to variations in the number of Pt-0 support bonds. The latter report featured special techniques to remove the predominating effects of Pt-Pt bonds. A Pt-0 bond at the appreciably different distance of 2.05 A was reported for reduced Pt/ alumina and was ascribed to internal oxide ( A l l ) . Support 0 to Pt bonds were reported at 2.65 A. These differences in the reported bonding distances to oxygen probably represent discrepancies that deserve resolution. Edge analysis was used in several studies to document the loss of Pt d electrons (e.g., ref A10, A12-Al4). The role of Re is fixing the Pt to the support was followed (AI5),and the rhenium valence was fixed at Re4+after reduction (AI3). In one study of Pt-Ni, an alloy was formed in which it was noted that a linear relation between nearest-neighbor distance and Ni concentration could not be applied (AI6). Observations on bimetallics have been extended to the pairs Cu-Os, Cu-Rh, and Ir-Rh ( A l 7 ) and Re-Cu, Ir-Cu, and Pt-Cu ( A I 8 ) . It was observed that the surface segregated component is the component with the lowest surface energy (Ir-Rh being somewhat exceptional though), and good mixing of the components can be observed throughout the full range of bulk miscibility down to complete immiscibility. Compositional dependence of structure for Fe-Rh/silica was demonstrated in a study combining EXAFS and Mossbauer emission spectroscopy ( A I 9 ) . At low Fe content, Fe atoms are mostly Fe3+ ions and thought to be located a t the Rhmetal/silica interface, and at higher amounts of iron, Fe atoms are found in the metallic state a t the surface of the metal particles. On the other hand, a study of Ir-Ru/silica indicates that the surface tends to be an Ir-Ru alloy on the surface of a Ir core (A20). On the basis of the XANES, it was also concluded that the Ir in Ir/SiOPand Ir-Ru/Si02 is somewhat electron deficient. This result was observed for Ir/SiOz and Ir/Al2O3in a separate study (A21). In the same study a particular XANES feature in Pt/Si02 was modeled by a transition to an empty antibonding state arising from metal-support bonding and using a multiple-scattering X a calculation. The use of XANES to determined state density was compared with Auger techniques for MnOz-based catalysts, and in this case, Auger was concluded to be more reliable (A22). Titanium in Tic& was found to distort and decompose in forming MgClz supported Ziegler-Natta catalysts (A23). In another study, a vanadium oxidation catalyst was found to be promoted strongly with phosphorus when P/V > 1, but it was shown that P was not inducing any structural change (A24). The structure around Go in a homogeneous carbonylation catalyst was investigated (A25),and a trigonal bipyramidal coordination sphere was inferred from the measurement of 0 1987 American Chemical Society

CATALYST CHARACTERIZATION Robin L. Au8Iermann received a BA in chemlstry from the University of New D r i s am in 1980 and a PhD in analytical chemistry from the University of Colorado in 1985. Her current research involves the USB of thermal anaiysis techniques for the characterization of catalysts. polymers. and geological materials.

MYSOIONarayana received a BSc in physics and chemistly in 1970. a MSCin physics in 1972. and a PhD in physics in 1977. all from Dsmania University. Hyberabad. India. He carried out postdoctoral research at Wayne State University and the University of Houston. His current research involves the use of soiulion and solid-state nuclear magnetic resonance techniques and electron spin resonance to Characterize Catalysts. polymers. and oils.

Auger electron Spectroscopy (AES) and scanning Auger microscopy (SAM) for the investigation of catalysis and cormrbn. and the use of extended X-ray absorption fine structure (EXAFS) in catalysis.

Roberl Szonlirmay received a BS in chemistry in 1971 and a MS in chemistry in 1973 from Youngstown State University and his PhD in analytical chemistry from The Ohia State University in 1978. His current research involves Surface and pore characterization usin0 Ohvsisomtlon and chemisorption technib"& A s research also involves the use of mathematical and moiecular modeling far the characterization of catalyst. mineral. and polymer surfaces.

Donald W. Hart received a BS in chemistry from NoRh Carolina State University in 1971 and a PhD from Princeton University in 1975. He joined Shell aner a postdoctoral position at the University of Southern California. in Which he used single-crystal neutron diffraction to study transition-metal hydrides. His work at Sheii has focused on the characterization of solids by a variety of physicai methcds. with current emphasis on the characterization of polymers and catalytic materials using small-angle X-ray scattering.

Sunny C. Tang received a BS in chemistry from Unlversity of Califwnia at LOI Angeies in 1971 and his PhD in inorganic chemistry from Massachusetts Institute of Technology in 1975. His current research involves the use of X-ray dmraction and melecular modeling techniques to characterize catalysts, minerals. and polymers. He is me coordinator of this review. to whom cormSpondence Should be addressed.

Paul B. HlmeLrb received a BS in chemistry tmm the University of California at sonoma in 1980, an MS in materiais science from the University of Virginia at Charlottesville in 1983. and a PhD in materiais science from Lehigh Universw in 1986. His current interest involves the characterization of CataiYStS and polymers by electron microsCOPY.

Richard M. Irwin obtained a BS in chemistry and a PhD in physical chemistry from Texas A&M University in 1973 end 1978. Postdoctorai Work at the University of @orgia in 1978 involved laser ~ p s n r o ~ c o pand y computer automation. He Worked in laboratory information Systems and infrared spectroscoPy for ARC0 Chemical in 1980. Re. Search interests currently include the application of in situ infrared and Raman techniques for characterization of rites and *l'"ct",es on cataiytica11y actiie surfaces.

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Randall C. Yoales received a EA In chemistry from the University of Vtah in 1981 and his PhD in physical chemlstry from the University Of California at Berkeley in 1985. His Current research inVolveS the surtace Charactemation of catalysts. polymers. and mi"erals using X-ray photoeiectron ~ p e c t r o s c u PY. Iow-Bnerw Iow-Bnergy Ion scatterm scattering, scannmg DV. scannma AUAUger miCrOsCopy. and secondary #on m a s spectrometry

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three Co-C honds at 1.83 A and two more at 2.13 A. In another study, the superiority of an alkoxide preparation technique for Co Tt02systems over impregnation was pinpointed as being ue to the formation of substantially smaller CosO, crystallites upon calcination (A26). Silica-supported Co-Rh was demonstrated to consist of bimetallic particles, and it was also inferred that Co enriched the particle's outer surface by observing the effects of oxygen chemisorption on the EXAFS radial distribution function (rdf) (A27). Catalysts of mixed Cu-Zn/alumina are useful for methanol synthesis and other reactions and have received substantial attention lately. They have been shown to consist of CuO and ANALYTICAL CHEMISTRY, VOL. 59,

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ZnO in the fresh catalyst, while activation forms Cu metal and ZnO (A28-A30). Measurements with in situ reactions show that at low temperatures the transformation of the Cu chemical state is reversible, while a t higher temperatures, it is irreversible due to the formation of much larger Cu particles (A30). A study was also made of Cu/silica prepared by using two routes: one starting from Cu(OAc),-H20,the other from tetraamminecopper(I1) (A31). The latter was determined to form binuclear complexes which were more active than the mononuclear species believed to form from the latter route. Another binuclear catalyst, silica-supported Mo, is active for oxidation of ethanol and has been shown to undergo reversible shortening of Mo-Mo and Mo-0 bonds during reaction (A32). The same group has explained the large differences in the catalytic activity of Ru/alumina and Ru silica in terms of specific metal-support bonding features in E AFS as well as IR and UV-Vis reflectance spectroscopy (A33). An unusual Rh metal-0 support bond is proposed to explain the observation of a weak feature in the rdf for Rh alumina (A34). This feature corresponds to Rh-0 a t 2.7 and is felt to be due to anionic 0 inducing a dipole in the Rh metal atom. The Rh/Ti02 catalyst is prepared by reduction a t relatively low temperatures, but with higher temperature reduction, it enters into the “strong metal-support interaction” (SMSI) state. The former state has been described as consisting of Rh coordinated to 0 a t 2.71 i% and with a mean coordination number of 2.5, and Rh bound to Rh a t 2.67 A and mean coordination of 3.1, while the SMSI state involves an average bond contraction of 0.04 i% and the appearance of a Rh-Ti bond a t 3.42 A (A35). At higher reduction temperatures, direct Rh-Ti bonding is observed a t distances shorter than that of stable intermetallics (A36). In another investigation, the active form of two methanol carbonylation catalysts formed by exchange into a zeolite was determined to be Rh metal particles (A37). The lower activity the catalyst based on RhC1, compared to a similar catalyst based on [RhCl(NH,),]Cl, was ascribed to early formation of larger, more stable oxides in the RhCl,-based route. Finally, it can be noted that most catalyst studies to date have attempted only to define the overall structure of the catalytic species as a necessary first step in studying the process of catalysis. Single-crystal studies have the advantage of starting from a well-defined catalyst structure and orientation, and so are better able to move ahead to study the bonding of reactants, intermediates, and products on the catalyst. Due to the low specific surface area of such systems, the experiment is necessarily done by one of the specialized surface sensitive (SEXAFS) techniques. The bonding of formate on Cu(100) was found to be symmetrically located at a 4-fold hollow site (A38). Methoxy was also observed, but its location could not be pinpointed, although the atop site was ruled out, and the group was found to be tilted to the surface normal. In a similar study, formate on Cu(ll0) was found to be atop ridge atoms and the angular orientation was investigated (A39). In a study of the X-ray edge structure only, methoxy was found to be tilted on Cu(llO), but the location was indefinite (A40). The tile orientation that was deduced in this study was not in agreement with the results of photoelectron diffraction (A41),and this discrepancy has yet to be resolved. Adsorption of CH3SH on Pt(ll1) has been studied, and two intermediates have been observed that exhibit tilted eometries, thiomethoxy (CH3S) and thioformaldehyde (SEH,) (A42). Thioformaldehyde is reported to be a stable species in contrast to formaldehyde on this surface. Further information on these subjects may be obtained by other available reviews of EXAFS of catalysts (A43-A45) and comparisons of SEXAFS and other surface analytical techniques (A46).

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DIFFRACTION, SMALL-ANGLE X-RAY SCATTERING, AND MOSSBAUER SPECTROSCOPY X-ray and Neutron Diffraction. X-ray diffraction plays

an important role in catalyst characterization, especially for monitoring changes in crystal structures, measuring particle sizes of supported metals, and identification of crystalline phases that occur during catalyst preparation and under reaction conditions. Applications of in situ X-ray diffraction, generally combined with other analytical techniques, are in70R * ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNE 15, 1987

creasing in popularity, not only for the kinetic information obtained, but because catalyst compositions under ambient conditions may differ from those under reaction conditions. The increasing availability of synchrotron sources, providing both very high intensities and a wide range of available wavelengths, is making possible diffraction measurements that have never before been possible. Zeolite unit cell sizes are very sensitive to changes in their aluminum content, allowing X-ray diffraction to be an accurate tool for measuring Si/Al ratios. This is especially important because the Si/Al rabo of the lattice, measured by diffraction, may differ considerably from the Si/A1 ratio of the bulk. Hydrothermal dealumination of the ultrastable and rare-earth Y zeolites (B1)show that the rate of aluminum removal and migration to the surface is initially very rapid but slows logarithmically with time. Loss of framework aluminum is linearly related to the rate that aluminum accumulates a t the surface. Chemical dealumination of sodium Y zeolite with Sic&(B2)also causes aluminum migration to the surface, with some extra-lattice aluminum remaining in the zeolite cavities. Refinement of neutron powder diffraction data taken a t 5 K from zeolite rho containing six xenon atoms per unit cell shows the gas to occupy positions in the center of octagonal prisms between supercages (B3). At 210 K, some xenon occupies a site just outside the octagonal prism, inside the supercage. X-ray diffraction data taken between 40 and 252 K on the same zeolite containing 0.9 and 1.7 xenons per unit cell (B4) confirm that the preferred site of adsorption is in the octagonal prism a t temperatures below 160 K. At these gas loadings, xenon is lost to desorption a t higher temperatures. In studies on zeolite-based catalysts, X-ray diffraction is generally used to follow changes in the structure of the crystalline framework. In a study of two Co ZSM-5 catalysts, the contribution of the zeolite to the total iffraction pattern was removed by using a Fourier technique (B5).The resulting undistorted diffraction patterns of cobalt-containing phases were analyzed in detail to obtain average particle sizes, particle size distributions, and estimations of stacking fault frequencies. In situ measurements monitored changes through calcination, reduction, carburation, and subsequent recalcination and reduction. The catalyst made by impregnation with cobalt nitrate formed larger metallic cobalt particles on reduction than did the catalyst produced by vapor-phase impregnation with cobalt carbonyl. Upon carburation, the carbonyl-impregnated catalyst produced unexpected quantities of COO that persisted through the following calcination and reduction steps. These results were explained in terms of particle sizes determined by line shape analysis. X-ray diffraction continues to be widely used to estimate crystallite sizes in supported group VI11 metal catalysts, from either line widths (B6-B8) or analysis of the complete profile (B9,BIO). These measurements are often done in conjunction with chemisorption and electron microscopy studies, as the various methods differ in their sensitivities to different size ranges. Particle size measurements by diffraction have the advantage that they may be done in situ. The phase formed by exposing palladium black to ethylene at 200 OC was shown by in situ ( B I I )X-ray diffraction to be a solution of carbon in palladium, not @-PdHas had been previously reported. The hydride phase is stable a t room temperature, but not under these reaction conditions. Formation of P-PdH and a solid solution of carbon in palladium was observed on an alumina-supported palladium catalyst during hydrogenation of acetylene in an ethylene/acetylene mixture inside a specially built in situ cell designed to do simultaneous diffraction and kinetic measurements (B12). Low metal loadings and broad diffraction peaks caused by small crystallites sizes complicate interpretation of diffraction data from many supported catalysts. Superior background removal may be achieved by taking advantage of anomalous dispersion. The scattering power of an element will change significantly when the X-ray energy is very close to one of the elements absorption edges. Diffraction due to a particular element may be isolated by taking the difference between patterns measured very close to an absorption edge and another energy approximately 50 eV away, as diffraction from other elements will remain essentially constant over such small energy ranges. Georgopoulos and Cohen (B13)exploited the high intensity and continually adjustable energy selection a t the Cornel1 High Energy Synchrotron Source to measure

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diffraction patterns of sup orted platinum crystallites. The anomalous dispersion tec nique allowed them to observe diffraction from a catalyat containing only 0.825% Pt as 12-15 A crystallites on Si02,providing far better data than could be obtained by conventional X-ray diffraction. Hydrotreating catalysts are used extensiveb in the petroleum industry. Active sulfided hydrotreating catalysts tend to be X-ray amorphous, so they are best studied by other techniques. Catalyst precursors, with the metals in an oxide form, and some experimental catalysts often contain crystalline phases that are identified and quantified by X-ray diffraction (B14-B16). Electron radial distribution functions calculated from diffraction data of sulfided silica supported W and W/Ni catalysts show features attributed to the interatomic distance between W and Si in the support (B17). In the bimetallic catalysts, the radial distribution function did not unambiguously identify the Ni location but did rule out the possibility of having nickel in a bulk nickel sulfide (Ni-Ni ca. 3.4 A) or intercalated in WS2 (Ni-W = 3.45 A). Chevrel phases, with the general formula M,Mo6Sg (M = Ho, Pb, Sn, Ag, In, Cu, Fe, Ni, Co), have hydrodesulfmzation activities comparable to unpromoted and cobalt-promoted MoSz catalys? (B18).The rhombohedral Chevrel phases have structures quite different than MoSz and were shown by X-ray diffraction to be homogeneous and stable under hydrodesulfurization conditions. Reactivity and sensitivity to surface oxidation are related to the size of the cation. Small-Angle X-ray Scattering. Small-angle X-ray scattering (SAXS) is useful in catalyst studies for determining particle or pore size distributions and direct measurement of surface area. Applications of small angle scattering have been largely limited by difficulties in interpreting data from samples containing more than two phases; typical catalysts contain three: support, void, and a supported metal containing phase. In some cases, the particle size distribution of the supported phase may be determined directly from the difference between scattering curves of the catalyst and support. This method was used to study Nylon-supported platinum and platinumtin catalysts (B19).It was shown that addition of tin reduces the average platinum particle size without altering the overall morphology. Interfacial surface areas between various phases may also be obtained from SAXS data if the volume fractions of the phases and their electron densities are known. In a study of platinum supported on titania, strong metal-support interactions produce significantly lower free metal surface areas than are found in “normal” catalysts (B20). An interesting extention of current methods for interpreting small angle data is a parameterization of amorphous systems in which the phase boundaries are characterized by their areas and angularities (B21). Although this method requires assumptions about the form of the parameterization, those choices that produce satisfactory fits give very similar results. In situ small angle X-ray scattering measurements of polydispersity in two Pt/A1203 catalysts agree rather well with thoses from electron microscopy (B22). The observation that sizes from X-ray scattering were slightly smaller than those from microscopy was attributed to surface oxidation of the samples that were exposed to air before being place into the microscope. A promising description of amorphous catalyst systems is based on the Voronoi model, in which space is divided randomly into polyhedral cells, each cell containing either pore, support, or the supported metal containing phase. The complete quantitative description of a catalyst requires only the volume fractions of the phases, known from chemical composition and density measurements, and the density, or average size, of the Voronoi cells, obtained by optimizing the agreement between observed and theoretical small-angle scattering c w e s . This analysis was applied to data collected between 400 and 700 “C with Pt/AlZO3.Observed redispersion of the metal at low temperatures followed by sintering at high temperatures is in agreement with static hydrogen chemisorption measurements (B23). Some improvement on the model may be obtained by using a correlated-cell model to account for the tendency for adjacent cells to be filled by the same phase. For Pt/Si02 and Pt/Al2O3and their supports, the correlated Voronoi model gave surface-pore interfacial areas good to a few percent and metal-pore areas correct to 1-2 significant digits (B24).

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Massbauer Spectroscopy. Mossbauer spectroscopy continues to be a powerful tool in catalyst characterization because of its specificity for single elements, providing information about oxidation states and local atomic environments. Although Miiasbauer spectroscopy is practical for only a few selected elements, the most common Mijssbauer isotope, 57Fe,is used in a variety of catalyst systems of commercial importance. Mossbauer spectroscopy is commonly used for bulk phase identification but is also a powerful tool for characterizing surface species and, in some instances, for measuring particle sizes. The relatively high penetrating power of the y radiation makes Mossbauer more amenable to in situ studies than many other analytical techniques. During this review period, two in-depth reviews relevant to catalytic applications of Mossbauer spectroscopy have been published. Montan0 (E%) reviews technological applications, with examples from Fischer-Tropsch synthesis and coal liquefaction. To soe et d. (B26) review 57FeMossbauer studies of 57Co-doped8o/Mo/AlZOzhydrodesulfurization catalysts. Conversion electron Mossbauer spectroscopy, because of its sensitivity to surface species, was used to study the mechanism of carbon deposition on metallic iron films in the presence of acetone/COz mixtures (B27). Two phases, wiistite (FeO) and cementite (Fe,C), contribute to the formation of carbon filaments. Cementite formation fractures the wiistite phase, enhancing acetone disproportionation by increasing the available surface area available for reaction. The carbon filaments grew from cementite crystallites. Reaction conditions for controlled low-pressure oxidation of iron foils, studied by conversion electron Mossbauer spectroscopy,XPS, and Auger electron spectroscopy, may be varied to provide a selection of surface oxides (B28).Vacuum annealing of the initial oxide overlay reduces the iron oxidation state. Increasing the annealing temperature from 300 to 675 K causes the initial Fe304to change to a FeO type structure, providing a systematic method of producing surfaces in the desired oxidation state. Activity remains high in studies of Fischer-Tropsch synthesis for the conversion of Hz/CO mixtures to hydrocarbons. Combined Mossbauer and X-ray diffraction studies on silica-supported iron nitride catalysts (B29)show them to be less readily carburized than catalysts containing only metallic iron. At early stages of the reaction, nitrogen loss is more rapid than incorporation of carbon. The rate of carburation increases, until after about 3 h under their reaction conditions, the system equilibrates at a composition of about Fez.ls (C-,mN0,13). As originally prepared, Fischer-Tropsch catalysts consisting of iron supported on alumina and thoria both contain hydroxylated ferric ion (B30). Upon calcination, however, iron on the alumina support is bound directly to the support, while on thoria, it is found primarily as a-FeZO3. In both cases, reduction gives a-Fe, although about 30% of the aluminasupported iron is found as a FeAlzO, spinel. In situ Mossbauer spectroscopy found that on both supports, a-Fe is converted to x-Fe5C2under Fischer-Tropsch conditions, with the spinel remaining unchanged. Metal-support interaction is also observed in iron supported on TiOz (B31).Reduction temperature has a significant influence on these systems. Reduction at 450 and 500 “C causes suppression of carbide formation and causes catalytic activity to be substantially less than that observed with reduction at 285 “C. Mossbauer spectroscopy shows the initial metal phases to be essentially the same as bulk metallic iron, indicating metal-support interactions are localized at the iron-titania interface. Different behavior was observed on titania-supported iron photocatalysts for reduction of nitrogen to ammonia (B32). These catalysts are not reduced and are calcined at somewhat higher temperatures than were used in the previos paper. Titania in catalysts prepared by either coprecipitation or impregnation is found as anatase when calcined at 500 “C and rutile when calcined over 800 OC. A t 650 “C, both anatase and rutile are formed, the composition depending on the iron content. Combined Mossbauer spectroscopy, ESR, and X-ray diffraction studies show the iron incorporated into both support phases as a solid solution of ferric ions. Iron in excess of its solubility limit goes into cakdytidy inactive pseudobrookite, Fe2Ti05. Dissolved ferric ion could be assigned as the active catalytic species in this system. ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNE 15, 1987

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In situ Mossbauer measurements during CO/H2 reactions were used to characterize a variety of mixed-metal iron catalysts supported on zeolite Y and ZSM-5 (B33). Formation of iron carbide phases, observed in the absence of a second metal or in the presence of Cu2+or Zn2+,was suppressed when Ru3+ or Co2+ion exchanged zeolite was used. In a more unusual application of in situ Mossbauer spectroscopy, local temperature increases in a silica-supported iron catalyst were measured during Fischer-Tropsch synthesis (B34). This measurement is possible because internal magnetic field strengths vary with temperature in a known manner, allowing the temperature to be determined from the magnitude of magnetic splitting in the Mossbauer spectra. €'-Iron carbide, formed under Fischer-Tropsch conditions, provides such a probe, showing local temperature increases of 13 and 19 "C measured at nominal bulk temperatures of 275 and 300 OC. The measurement gives bulk crystallite temperatures of only a single phase, so it may not be representative of all of the iron species and does not measure the actual surface temperatures. The results are very important, however, in that the observed temperature variations are clearly large enough to introduce significant errors in thermodynamic data calculated from bulk temperatures. Niemantsverdriet et al. have carried out extensive Mossbauer studies of bimetallic Fe-group VI11 metal catalysts (B35-B37). In 1:l Fe/M (M = Ru, Rh, Ir, Pt) catalysts, reduction gives FeM alloy and highly dispersed ferric ion. Fe/Pd, however, shows almost complete reduction to FePd alloy and a-Fe. Reduction of ferric ion to ferrous upon ammonia or carbon monoxide chemisorption is monitored by changes in the Mossbauer spectroscopy. In situ Mossbauer and methanation kinetic studies of 1O:l Ni:Fe on alumina or titania (B38)show reduction produces FeNi alloy and ferrous ion on both supports, with greater quantities of Fez+on alumina, in line with the general observation that metals are more readily reducible on reducible supports than on irreducible supports. Exposure to H2/C0 causes an increase in Fe2+and loss of FeNi on both supports. On TiOz, the ferrous ion may be reduced by hydrogen, while on A1203,Fez+remains mostly unchanged during treatment in hydrogen at 500 "C. Differences in spectroscopic and catalytic activities are explained in terms of titania-containing surface species on the supported metal. Internal magnetic field strengths of superparamagnetic phases depend on crystallite size, making possible particle sizes estimates by measuring magnetic splitting in Mossbauer spectra as a function of external magnetic field strength. Although superparamagnetism is far less common in a-Fe than iron oxides, it is possible to make small, superparamagnetic a-Fe crystals on carbon supports (B39). Because of their average diameter is only 25 f 2 A, these iron particles have about one-third of their atoms on the surface. In spite of this, except for the superparamagnetic properties, Mossbauer shows them to be essentially the same as bulk a-Fe. Mossbauer studies in catalysis have been dominated by work on iron-containing materials because iron is clearly the most common of the limited number of Mossbauer-active elements that is used extensively in catalysts. Tin, sometimes used to modify catalytic activity, may also be studied by Mossbauer spectroscopy. Mossbauer spectroscopy, chemisorption, and thermal analysis were used to study the effects of tin on supported iridium catalyst used for cyclohexane conversion (B40). The majority of the tin in this system exists as Sn(0) alloyed with iridium. In the absence of tin, cyclohexane dehydrogenation is accompanied by a substantial amount of hydrogenolysis. Tin improves selectivity for benzene by suppressing hydrogenolysis and also dramatically decreases the activation energy for dehydrogenation. These observations are consistent with a ligand effect between tin and iridium.

NUCLEAR MAGNETIC RESONANCE 27Aland 29Si NMR. During the past few years, aided by the rapid progress of pulsed NMR techniques, numerous reports of solids characterization by silicon and aluminum NMR have appeared in the open literature. For an exhaustive review of this area, there are several excellent review articles by Thomas, Klinowski, and others (C1-C5) covering about 500 references to zeolites, silica-alumina, sheet silicates, and their pillared variants. Another review by Kokotailo et al. (C6) 72R

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containing 67 references specifically addresses the structural changes in zeolites before and after various dealumination procedures. Pinnavia et al. (C7) studied, by aluminum NMR, pillaring of smectite clays. They conclude that irrespective of the differences in the pillaring reagents, the same type of oxo cations, probably Al13Keggin ions, are formed on the intracrystalline surfaces of the clays. Deposition of an uniform monolayer of hydrated polyoxo cations in the interlayers is proposed with the concomitant achievement of electrical neutrality via the hydrolysis of the pillared cations. Anderson et al. (C8) showed with the aid of NMR and IR spectroscopic techniques that treatment of highly siliceous ZSM-5 zeolite with aluminum chloride vapor a t elevated temperatures results in isomorphic substitution of A1 for Si in the framework with the simultaneous formation of octahedral aluminum ions a t the nonframework sites. Nakata et al. (C9) used silicon and aluminum NMR in the chemical structural analysis of Y zeolites and mordenites. They showed that while proton exchange of the Y zeolites results in simultaneous dealurnination, such is not the case with the mordenites. This comparison may not be meaningful since the Y zeolites are much more aluminum rich than the mordenites are and thus more susceptible to dealumination. However, from the studies of Aukett et al. (CIO) it follows that even in a high silica zeolite such as a ZSM-5 with Si/Al 15, dealumination can occur on proton exchange. It is interesting to note that part of this nonframework aluminum goes back into the framework during alkylation reactions. Geurts et al. (C11) demonstrated the usefulness of the relatively new technique of nutation NMR in characterization of zeolites. From the changes, dependent on the extent of hydration, they concluded that most of the aluminum ions in HZSM-5 are in highly symmetric surroundings. The presence of a second type of aluminum species, whose spectra were independent of the hydration status, was observed which would have escaped detection with routine NMR methods. Fyfe et al. (C12) addressed the controversial issue of similarities between silicalite and ZSM-5 by 57Al and 29Si MASNMR (magic angle spinning NMR). Their studies indicate the two zeolites to be isostructural and that by various dealumination procedures ZSM-5 could be converted into silicalite. Scholle et al. (C13) attributed their observation of several distinct tetrahedral aluminum species in the aluminum NMR of TPA-ZSM-5 zeolite to the presence of the tetrapropylammonium cations in the zeolite pores. Jacobs et al. (C14)studied the solid transformations occurring in the ZSM-5 zeolites during thermal treatment. Based on the aluminum and silicon NMR data, they postulated that dealumination results in migration of aluminum ions from framework to interstitial positions, thus relieving the strain from the four-membered rings. Consequently the pore intersections become more open. Their realumination data indicate similar phenomena occur in the reverse direction. In similar studies with TPA-ZSM-5 zeolites, Engelhardt et al. (C15) observed a new silicon resonance at -98 ppm and assigned it to Q3defect centers [SiO-1. Haller et al. ('216, C17) showed by 27Al solid state MASNMR methods that there are distinct surface aluminum species present on the Ni-Mo-P/A1203 hydrodesulfurization catalyst. Calcined Mo/A1203 showed the formation of aluminum molybdate which was not seen on Ni-Mo-P/A1203. The formation of AlPO, on such a catalyst is suggested. Aluminum and silicon NMR were used by Plee et al. (C18, (219) to define the short range order/structure in pillared smectites. Calcined pillared smectites showed no reaction between the pillars and the clay in the absence of tetrahedral substitution (hectorite and laponite). In beidellite, which does have such a tetrahedral substitution, a deep structural transition was observed upon calcination. It was interpreted to be a growth of a three-dimensional network grafted on the two-dimensional network of clay, the final product having acidic properties comparable to zeolites and significantly stronger than those of calcined pillared smectites without substitution in the tetrahedral layers. An independent study by Diddams et al. (C20) drew similar conclusions about the increased acidity/activity of beidellite-smectite clays compared to montmorillonite-smectite. A useful review of NMR studies of graphites and sheet silicates, in the context of the role of intercalates in heterogeneous catalysis, is given by Jones


et al. (C21). In this study aluminum NMR was used to establish the role of exchangeable cation, some of them being A P , in determining the acidity of the catalyst. Welsh et al. (C22) characterized amorphous silica-aluminas by 27AlNMR. They demonstrated the uniqueness of this technique in structure determination of these amorphous materials, in particular with reference to differences in preparative procedures. The chemical shift differences between the octahedral and tetrahedral aluminum species changed with the surface area which also changes the tetrahedral/octahedral ratio. They postulated that the chemical shift differences of the tetrahedral peak with reference to that in an aluminum-rich zeolite can be explained in terms of dilution of the tetrahedra in the amorphous materials. Grobet and Jacobs (C23) studied the ultra dealumination of Y zeolites, silicon tetrachloride treatment followed by HCl reaction and steaming, by silicon and aluminum NMR. Microstructure of this highly siliceous zeolite with Si/A1 70 is discussed. Engelhardt and Lohse (C24) examined the controversial hypothesis of Breck and Skeels regarding reinsertion of aluminum into zeolite framework. They claim that NMR and IR do not support such reinsertion. However, this point seems to be still open for debate as other groups have made counterclaims regarding such restoration of framework aluminum under some very specific treatment conditions. Cross polarization and Si MASNMR were used to obtain the structural description of diphenylphosphinoethylsilyl ligand anchored on silica gel surface. Based on HPLC and NMR data Rudzinski et al. (C25) suggested that their synthetic procedure of immobilizing diphenylphosphine moieties is the most effective method. 13CNMR. Ford et al. (C26) reviewed the NMR methods used in characterizationof catalysts supported on cross-linked polystyrene and silica gel. The precautions necessary to make the NMR spectra quantitative were addressed. Ethylene insertion into soluble Ziegler catal sts was examined by NMR techniques (C.23. By the use of &-enriched ethylene, Fink et al. concluded that there is no precoordination of the monomer in the primary complexes and that the monomer insertion occurs unambiguously directly in the Ti< bond. Nagy et al. (C28) showed that 13CNMR of adsorbed propylene gives direct insight into the nature of the pores, texture of the catalyst, and into the interaction of the surface with the adsorbed molecules. They showed that the NMR measurements can augment the information obtained from conventional BET measurements in characterization of catalyst surfaces. Wang, Slichter, and Sinfelt (C29)have addressed structure determination of adsorbed ethylene on small platinum clusters by using spin echo methods. The formation of an ethylidene species (C-CH3) was proposed to explain their observations. The catalytic hydrogenation of CO was studied (C30) by 13CNMR of CO adsorbed on ruthenium exchanged Y zeolite. The authors conclude that adsorption at room temperature results in linear and dicarbonyl species. The observation of COPin the spectra is attributed to oxidation of CO by residual metal oxide on the catalyst. Duncan et al. (C31) also used solid state MASNMR methods to characterize silicasupported ruthenium catalysts and they concluded that one of the proposed alkyl intermediates in CO hydrogenation is a linear alkyl species bound to Ru metal. They also showed, based on transient NMR, that purging the catalyst with helium converts this intermediate into another reactive alkyl intermediate precursor to methane. Derouane and Nagy (C32) reviewed the advantages in using carbon NMR in obtaining quantitative information concerning reactions on zeolites and other catalytically active oxides (e.g., butene isomerizationon Sn-Sb oxide). They reviewed the information, obtained by 13CNMR methods, about the adsorbatesurface interaction in general and methanol conversion on ZSM-5 zeolite in particular, with the latter being a clear demonstration of surface methylation. The advantages of the NMR techniques were elegantly demonstrated in the study of isomerization of butenes over NaGeX zeolite. Takahashi et al. (C33) showed that the CO-Rh interaction is much stronger in a zeolitic catalyst than on a silica based catalyst. Quantitative I3C NMR measurements were used by Mohammed et al. (C34) to derive statistical average structure parameters of a reduced crude (Iraq) and its hydrotreated products (commercialNi-Mo/A1203). An inverse correlation was observed between the behavior of saturated hydrocarbons

-

and aromatics, with higher operating temperatures favoring alkyl aromatics. The formation of naphthenes was found to be well correlated with first-order kinetics with an apparent activation energy of 23.6 kJ/mol. The importance of specifying the operating conditions as well as the nature of the crude in judging the performance of the catalyst is well brought out in this work. Sullivan (C35) discussed the use of multinuclear solid state NMR techniques in characterizing the catalysts as well as the residues. It is shown that the commonly used side band suppression sequence (TOSS) significantly distorts the apparent aromatic to aliphatic ratio. Possible methods to better characterize the aliphatic portion of the residue/coke are discussed. Using 13C NMR, Liang and Gay (C36) showed that until the stage of decomposition, the only chemisorbed species on MgO catalysts is a methoxide species. A bicarbonate or a H-bonded carbonate is postulated to be the decomposition product on the catalyst. Kuznetsov and co-workers (C37) studied the interaction of carbon monoxide with hydrogen over rhodium/lanthanum oxide catalyst. Their results indicate that depending on the CO/H2 ratio, carbonyl groups are transformed into alcohols, ethers or acids, and esters. An excellent review of solid-state carbon NMR techniques applied to characterization of derivatized surfaces is given by Thomas and Klinowski ( C I ) . Acidity. Dessau and Kerr (C38) studied the strong shape selective acid sites generated in ZSM-5 and ZSM-11 zeolites by successive treatments with aluminum chloride, hydrolysis, and calcination. NMR and IR data are used to support reincorporation of A1 in lattice sites. From the aluminum NMR and the FTIR data they concluded A1 does indeed get incorporated into the framework which was further confirmed by catalytic and ion exchange studies and temperature-programmed ammonia desorption. Lunsford, Rothwell, and Shen (C39) introduced trimethylphosphine (TMP) adsorption as a new and sensitive method to probe acid sites. By using phosphorus (31P)NMR these authors were able to distinguish T M P bound to Bronsted or Lewis sites on HY zeolite. These assignments were found to be consistent with IR data. Since 31Pis 100% abundant spin bearing nucleus and quite easy to detect, this new approach to measure acidity can be completely quantitative and can be used as a complementary technique for the conventional optical methods. Pfeifer et al. (C40) reviewed the various NMR techniques used to study quantitatively acidity of zeolites and related catalysts. Through magic angle spinning of thermally activated and sealed samples, they have been able to quantitatively determine the concentration of nonacidic hydroxyl groups and of residual ammonium ions. They concluded that in contrast to Bronsted acidity, these NMR methods become too complex to study Lewis acidity because of experimental difficulties, primarily caused by fast exchange of adsorbed bases between different adsorption sites. Freude (C41) reviewed the NMR line broadening effects, in the context of surface acidity of HY zeolites, in terms of magnetic dipole-dipole interactions and the quadrupolar interaction. Nagy et al. (C42) studied the effects of acidity in the isomerization of n-butenes on mixed tin-antimony oxide catalysts. From the I3C NMR data they concluded that both acidic and basic sites are involved in the stabilization and transformation of the adsorbed butenes. A cyclic type intermediate was proposed to account for all the experimental results. Mastikhin et al. (C43) measured the chemical shifts of protons from the hydroxyl groups on silica, alumina, aluminosilicates, phosphates, and ZSM-5 zeolite. These were compared with IR spectroscopic data and residual charges were calculated by quantum chemical methods (MIND0/3). Wendt et al. (C44) studied the surface chemical properties of precipitated NiO/SiO A1203 catalysts and the corresponding carriers alone. &n the basis of 'H NMR, IR, and NH3 adsorption measurements, they concluded that the number of Lewis acid sites increased on incorporation of Ni on the carriers even though the number of hydroxyl groups does not change significantly. With increasing alumina content, the strength of the Lewis sites increased and Bronsted sites were detectable at very high alumina content. Occelli et al. (C45) monitored the surface acidity of synthetic offretite and ZSM-34 by 'H NMR and IR. ZSM-34 was shown to be more selective to conversion to ethylene while offretite ANALYTICAL CHEMISTRY, VOL. 59, NO. 12. JUNE 15, 1987

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makes more propylene and heavier olefins in the catalytic conversion of methanol. They claim to have been able to distinguish the distinct differences among the charge-compensating protons and classify them into three categories: isolated protons with average interproton distance of 10 A, localized pairs of protons with an average internuclear distance of 7 A, and clusters of protons with internuclear distance of 3 A. Ashton et al. (C46) described the acidity of faujasite zeolites in terms of a structure parameter associated with the distribution of aluminum in the framework. They conclude, on the basis of MASNMR, surface analysis, and TPD of NH3, that the observed activity in HZSM-5 catalysts depends on an appropriate balance between nonframework and framework aluminum. No specific function for the nonframework aluminum is given. Other Nuclei and Studies. Ledoux et al. (C47) used 59C0 NMR (a seldom studied nucleus because of strong quadrupolar interactions) to characterize hydrodesulfurization catalysts. Four different cobalt sites were observed. They interpreted the results in terms of a new quasi-amorphous cobalt sulfide phase coexisting with the regular Cogs8phase, with Co inside very irregular tetrahedra of sulfurs. Such a configuration can be in dynamic equilibrium with an inactive octahedral cobalt with two vacancies in its coordination sphere. The authors conclude that the so-called synergistic effect of Co on Mo can be simply interpreted in terms of additivity of MoS, phase .. to. that of this new highly dispersed tetrahedral cobalt activity sulfide phase. Schlup and Vaughan (C48, C49) investigated fluorinated silica, alumina, and aluminosilicate catalysts using fluorine and hvdrogen NMR: aluminum-bound fluoride ions were observed i n fluorinated alumina, while only silicon-bound Fwas seen on the aluminosilicates with less than 25 wt % of alumina. NMR data obtained with the CPMG (spin echo) sequence indicates that the hydroxyl groups and fluorine atoms are isolated from like nuclei for aluminosilicates having fluorine concentrations up to 5 wt %. No alumino-oxyfluorides were detected. Boron ("B) MASNMR was used as a complementary technique to nAl NMR to confirm the substitutional insertion of boron into the zeolite framework for samples treated with BC13. From these NMR data and the test catalytic reaction of cracking of hexane, Derouane et al. (C50) concluded that activity is governed by the framework tetrahedral aluminum content. The critical variables in the NMR experiments to quantify aluminum are discussed and a mechanism is proposed to account for the acidity of the modified zeolite. The effect of hydration and dehydration on the coordination of boron in H-boralite was investigated by Scholle and Veeman (C51)by llB MASNMR. A substantial effect is observed via the quadrupole interaction which implies that dehydration severely distorts the coordination sphere of boron to the extent that boron almost lies in the plane of three 0 atoms. Sanz, Rojo, and co-workers (C52, (2.53) studied the adsorption of hydrogen on reduced C13Rh/TiOz catalysts. The new line a t high field (with reference to the surface OH) is assigned to hydrogen adsorbed on metal particles. Loss of intensity of this line in samples reduced at >723 K is ascribed to strong metal-support interaction (SMSI). The adsorption of the most labile H on the metal is accompanied by a hydrogen transfer to the support. They suggest that incorporation of H to the support is favored when the sample temperature is increased above 400 OK. However, these authors do not address the fact that some of the hydrogen is associated with paramagnetic Ti3+ions, incidentally formed during reduction, and such hydrogen would escape NMR detection under normal conditions. In similar studies on Rh/V,05 and Rh/TiOz-V205, Miller, Dybowski, and co-workers (C54, C55) concluded that the spillover H atoms are active in hydrogenation reactions. Claque (C56) reviewed the solid-state NMR studies and NMR spin imaging of materials such as coal, cements, minerals, and polymers. Elchior et al. (C57) applied 29Siand 7Li MASNMR methods to elucidate cation placement effects in a series of partial1 exchanged Li,Na-A zeolites. It is shown that the average BSi chemical shift is not a linear function of fractional lithium exchange and can be interpreted in terms of preferential occupation of specific cation sites by Li+. Arguments are given for local as well as long range order in the arrangement of cations as a function of hydration of the 74R


zeolite. Boxhoorn et al. (C58) studied a number of ZSM-5 and ZSM-11 zeolites prepared with a wide variety of bases by 13C and 29SiMASNMR. The study confirmed the presence of occluded organic cations a t the intersections of the 10-ring channels in the zeolite. The splitting observed for the methyl resonances is shown to be related to the ZSM-5 channel structure. The nature of Si NMR spectra is shown to depend strongly on the presence of silanol groups, confirmed by cross polarization studies, in specific defect positions in the zeolite lattice. Makowka and Slichter (C59) observed l&Ptfrom resonances in the surface layer of small platinum metal particles (supported on 7-A1203)on which 13C0 was chemisorbed. They used the elegant technique of spin echo double resonance between lg5Ptand 13C to differentiate between the surface platinum atoms from bulk platinum atoms. The authors proposed a model to account for the small surface Knight shifts and the structure seen in the platinum NMR resonances. Xenon NMR ('%e) was used by De Menorval et al. (C60) as an NMR probe to determine quantitatively the distribution of CO, chemisorbed on small platinum particles dispersed in the supercages of NaY zeolite. In similar work involving Ni-Nay, based on xenon NMR data, Scharf et al. (C61) concluded that the migration of nickel during reduction to the external surfaces of the zeolite is not reversible by subsequent oxidation. Exchange reactions of CzH6and other small molecules with deuterium over platinum or rhodium supported on silica were monitored by deuterium NMR. Brown et al. (C62) concluded that the usual stepwise and multiple exchange mechanisms are not sufficient to explain the results in particular with the rhodium catalysts. In similar work involving a coal liquification catalyst, Yokono et al. (C63) invoked the acidic properties and concentration of Mo5+on the catalyst to explain the H-D exchangeability,with specific reference to anthracene. Hasha et al. (C64) investigated the molecular mobility of benzene (de)in X zeolites by means of deuterium NMR. Steric effects and specific ion-benzene interactions are discussed. The 170and 51NNMR spectra were utilized (C65) in the characterization of a SO oxidization catalyst. Debras et al. ('266) used ?Si, nAl, and &3 Na NMR techniques to characterize pentasil type materials synthesized by various procedures. They attribute the changes in the Si NMR spectra to crystallographic changes of the zeolite, from orthorhombic to monoclinic form, when the Si/Al ratio was greater than 35. They correlated this change to the rearrangement of interior SiOH groups, which are clearly observed by cross polarization methods. Nagy et al. (C67) reviewed high-resolution multinuclear NMR of adsorbed molecules on zeolites and other heterogeneous catalytic systems. Hoffmann et al. (C68) evaluated by NMR, IR, TPD, and catalytic experiments the variations introduced by ion exchange of Mn2+into NaY and HNaY zeolites. They attributed the higher acidity observed in the zeolite with manganese to specific sites with MnX+.Further support for this hypothesis was given by calculations of partial changes on the basis of Sanderson electronegativity concept. Stokes (C69) described in very useful detail the roblems involved in characterizing Pt/Al2O3catalysts by l99Pt NMR and how to circumvent some of them. The effectiveness of spin echo double resonance method to separate out the bulk vs. surface species is highlighted and the chemical shifts of a number of platinum compounds are discussed. Ione et al. (C70) explored the possibility of hetero substitution of the silicon atoms in the zeolite framework sites to change the catalytic activity. They showed that the probability of such substitution can be predicted on the basis of Pauling criteria. NMR of 9Be, llB, and 71Gaand ESR of Fe3+ were used to characterize these newly synthesized zeolites.

ELECTRON SPIN RESONANCE The applications of electron spin resonance (ESR) to heterogeneous systems including determination of oxidation states, monitoring ion migration, and formation of ion pairs have been reviewed by Che and Ben Taarit @ I ) . Emphasis is given for the determination of the nature of catalytic site and its coordination number (56 references). Shvets (02) reviewed the application of ESR and UV spectroscopy in the study of coordinatively unsaturated transition-metal ions on catalyst surfaces (190 references).


Zeolites. 1-Butene activation of a Ni2+-exchangedfaujasite-type zeolite catalyst for the dimerization of ethylene was studied by ESR (03). Reduction of the divalent nickel ions by the olefin results in Ni+ (easily detectable by ESR) which is proposed to be the active center. A reaction mechanism involving the formation of H- is proposed. Kucherov et al. ( 0 4 ) carried out an ESR study of cupric ion exchanged H and Na forms of mordenite (HM and NaM) and ZSM-5 zeolites. In HM with low percentage Cu, Cu2+ions are isolated and in square pyramidal coordination. These ions were found to be resistive to CO treatment below 400 "C. Clustering of cupric ions was observed in Cu-HM for high cation content with the concomitant increase in the ease of reducibility by CO at 300-400 "C. In contrast negligible clustering was observed in ZSM-5, with the cupric ions located in two different isolated positions, in square planar and pentacoordinated environments. The coordinative unsaturation of cupric ions in both zeolites is confirmed by the observed stron influence of CO and O2 on the hyperfine couplings of CUB. Most unusual was the observationthat the calcination of HZSM-5 with Cu powder in air resulted in migration of isolated cupric ions into the zeolite channels. This may be a new method of incorporating ions of interest into the zeolite lattice. Narayana and Kevan (05)used ESR and electron spin echo modulation techniques (ESEM) to study the site location and environment of cupric ions in CdX zeolite. A trigonal bipyramidal complex is proposed to account for the observed spectral features, with the most probable location being six ring windows between the sodalite and supercages of the zeolite. The similarities and difference between Cu-CdX and Cu-CaX are discussed. In similar studies, Michalik et al. (06) followed the formation of monovalent nickel ions and their interactions with various inorganic and organic adsorbates in Ni-CaX zeolites by ESR. The formation of two new Ni+ complexes involving Hz are postulated, both being stable only in the presence of hydrogen in the zeolite. The reversibility of the observed number of Ni+ spins is attributed to ion pair formation. A planar complex with ammonia and a compressed tetrahedral or pyramidal arrangement with adsorbed ethylene are reported. In contrast, adsorption of water or methanol formed distorted octahedral complexes. Kucherov and Slin'kin (C7) studied the formation of radicals on adsorption of alkenes on H-mordenite. The center responsible for the radical formation is proposed to involve both the Bronsted acid sites as well as redox sites, the former's participation being confirmed by the decrease in radical formation in catalysts pretreated with NHB. The redox sites are thought to be formed due to rupture of a strained Si-0-Si linkage in the four-membered rings of mordenite structure. ESR study of carbon deposits on hi h silica zeolites (08) during methanol conversion indicate the formation of two distinct types of coke. From this study Kalinina et al. concluded that the condensed carbonaceousform, which appears above 923 K, is responsible for the complete deactivation of the catalyst. The chemical state of palladium in Pd-NaX zeolite was determined by ESR and XPS methods (09). Oxidative calcination of the zeolite ion exchanged with palladium tetraminechloride indicated the formation of trivalent palladium ions which could be reduced very easily to monovalent palladium ions a t moderate temperatures. ESR and XPS data indicate the formation of small charged clusters which could not be unambiguously identified. Zina et al. (010) characterized the reduction of Pd-NaY zeolite by ESR methods. Hydrogen or ethylene reduction of Pd-NaY at 25 OC (after pretreatment with O2 at 500 "C) transformed the Pd3+ions to Pd+ species stabilized in sodalite cages. Above 150 "C inaccessible divalent palladium ions were reduced to a different Pd+ species with the simultaneous formation of some metallic Pd. Treatment with carbon monoxide at 25 "C resulted in formation of Pd+(C0)2in the supercages. Reduction to metallic state was observed above 250 OC. Interactions of the paramagnetic palladium species with with various adsorbates were studied by Michalik et al. (D11) the aid of ESR and ESEM spectroscopy. Adsorption of water or oxygen resulted in almost identical 0-based paramagnetic radicals indicating decomposition of HzO by Pd3+. Various possible locations and coordination geometries of Pd ions in CaX zeolite are discussed. In related studies involving Pd-

cf

~

NaX (012),stabilization of the trivalent palladium ions inside the hexagonal prisms is postulated. The major differences in the formation and location of the palladium species between Pd-NaX and Pd-CaX zeolites are correlated with the site preferences of the major cocations present in these zeolites. The dimerization of ethylene catalyzed by Pd-CaX zeolite was investigated in the 280-403 K range by GC and ESR methods (013). The observed reverse temperature dependence of the rate of reaction was attributed to migration of Pd cations to inaccessible sites at higher temperatures. The influence of the major cocation on the activity of Pd was also investigated and it is concluded that the presence of divalent cocations promotes dimerization of ethylene even a t low concentrations of Pd a t relatively low temperatures. Under the same conditions the palladium zeolites with monovalent cocations are shown to be completely inactive for dimerization of ethylene. Goldfarb and Kevan (014) described the ESR and ESEM characterization of Rh-NaX zeolite. A Rh species exhibiting dynamic Jahn-Teller effect was observed and is proposed to be interacting with two hydrogen molecules in the supercages of the zeolite. The formation of other paramagnetic species on oxidation of the activated rhodium zeolite is described. The Claus reaction was investigated by in situ IR and ESR with X and Y zeolites as catalysts ( 0 1 5 ) . Acidic OH groups were seen on the X but not on the Y zeolites during the reaction. It appears that the chemisorbed SOz (observed by IR) and the SO2 radicals (observed by ESR) are not correlatable. Karge et al. (016) attempted to correlate the coke formation during alkylation and other reactions over dealuminated mordenitesby in situ IR and ESR. A consistent trend was observed between the S i / A ratio, the number of Bronsted sites and the coking tendency of the mordenite catalysts. It was not possible to establish a simple relation between the oligomeric radicals (with hyperfine coupling) seen at low reaction temperature and the isotropic coke signal seen at higher temperatures even though the oligomers could be the precursors of the coke radical. Bandiera et al. (D17) examined the conversion of methanol on mordenite, dealuminated mordenite, and ZSM-5 zeolites. Radicals generated by adsorption of NO or anthracene on activated samples were measured by ESR to estimate the acidity of the catalysts as complementary tool to IR measurements. The authors assi ned these radicals to adsorbed species at Lewis sites. It is cfemonstrated that as acidity of the catalysts is decreased by dealumination of the zeolites, selective conversion of methanol to olefins occurs. Due to the smaller number of acid sites, hydrogen transfer reactions become limited which reduces the coke formation irrespective of the channel size. When a larger number of acid sites are present, appreciable hydrogen transfer occurs promoting formation of paraffins and aromatics, carbonaceous residues rapidly build up in a large pore zeolite like mordenite and poison the catalyst. It is interesting to note that these authors found a ood correlation in the acidity of the catalyst as measuref by IR vs. ESR methods. Oxygen-Based Radicals. The role of 1 7 0 isotope in the characterization by ESR of adsorbed oxygen species on oxide surfaces was reviewed by Che et al. (CIS). The nature, structure, and reactivity of the 0 species is described in useful detail. Blasco et al. (019)studied the paramagnetic species formed after photoadsorption of oxygen on a RhC13/TiOz catalyst activated at different temperatures. As compared with oxygen adsorption in dark, UV irradiation leads to the generation of new oxygen radicals as well as to a lowering of temperature at which different steps of reduction of rhodium takes place under vacuum. From the thermal stabilities observed for the 0- radicals, Volodin (020)concluded that above 420 K, 0are most stable on the MgO surface. Below this temperature a complex lO-.O2)is proposed. Kuli-Zade et al. (021) studied by ESR the propene reaction with 0, adsorbed on titania or silica. The reactivity of 0; on TiOzis shown to be significantly higher than on silica. Sass et al. (022) examined the formation and reactivity of 02-on supported catalysts Ce/A1203and Ce-Pd/A1203 by ESR methods. The rate constants of the reactions of this radical with CO and ethylene on the mixed metal catalyst were found to be 1 or 2 orders higher than that on Ce catalyst. Beringhelli et al. (023)used ESR to characterize the pyrolysis ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNF 15, 1987

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products of cobalt carbonyl and rhodium carbonyl supported and 51VNMR indicated the presence of tetrahedral V5+. In on alumina or zirconia. Paramagnetic Rh(I1) species were flowing butylene, ESR showed the presence of vanadyl ions observed on Rh/yA1203. The hyperfine couplings indicate in the catalyst. The conversion was seen to decrease when metal-metal interactions. No paramagnetic species were seen the catal st got reduced beyond 22% level even though it remainedfselective to 1,3-butadiene. Mori et al. (033) infor cobalt carbonyl on either support. Irrespective of the vestigated the dependence of activity as well as selectivity in carbonyl used, contact with oxygen yielded an 02-strongly interacting with the support ion (aluminum or zirconium) the oxidation of benzene on the structure of unsupported and along with the oxygen radical anions bound to the supported supported V20, catalysts. The activity was mainly determined rhodium. The bond strength of the radical interacting with by the number of V O species on the supported catalysts while the selectivity for maleic anhydride was determined by the the support was correlated with the catalytic activity of these increasing markedly up to five layers number of layers of Vz05, systems. Howard et al. (024) studied the oxygen-copper interaction on Cu oxidation catalysts by a very novel method and attaining a constant value above. of monitoring the reaction of O2 with Cu3 and Cu5 clusters Kakuta et al. (034) reported the preparation of novel bi(matrix isolation) at 77 K. The clusters were formed by nuclear Cu catalysts active for the oxidation of CO with nitrous photoexcitation of copper atoms on the surfaces of frozen oxide. The catalysts, prepared by impregnation of silica with adamentane or cyclohexane. The 02-species is assumed to cupric acetate solutions, were characterized by ESR and IR. form by electron transfer from the Cu to the lrg*orbital of Significant amount of Cu pairs were estimated from the spin oxygen (with back donation to metal). Cluster geometries were concentrations measured in ESR and the rate of oxidation found to change by such electron transfer. of CO with N20 was found to be a function of the number of Gesser and Kruczynski (025) examined the role of hyperbinuclear species. The importance of the hydroxyl group in in the reduction of palladium-supported porous oxide (02-) anchoring the CU(OAC)~ complex on silica is stressed and a titania glass. Annealing at below 550 "C was found to stabilize reaction mechanism for the oxidation of CO with N20 was a high concentration of radicals. ESR data indicated that proposed on the basis of the binuclear structure of Cu ions. Poluboyarov et al. (035) suggested that fine dispersion of CuO these species can be displaced by bases such as ammonia and is in dynamic equilibrium with O2gas. Palladium photodeand Cu-0-Cu clusters in the systems CuO/MgO and pmited on the surface has little effect on the properties of 0;. CuO/A1203can be achieved by their reactions with thionyl However, Pd supported on amorphous Ti02 reacts with h chloride and antimony pentachloride in the presence of hudrogen at room temperature and low pressures producing TiYi midity. The reaction products exhibit Jahn-Teller effect in centers with concomitant destruction of the oxygen radicals. their ESR spectra. It is interesting to note that if the 02-is displaced prior to Kiwi and Prins (036) demonstrated the presence of Ru3+ hydrogen exposure, reduction of the support is retarded. ions in a RuOz/TiOz highly dispersed catalyst. A model is Xu et al. (026) studied the role of tetraalkyltin compounds proposed for the mode of intervention of RuS+ Ru4+states in the metathesis of alkenes catalyzed by supported rhenium in oxidative processes. Bonnviot et al. (037) iscussed the catalysts. ESR of such a system revealed that the alkyltin formation of monovalent nickel ions by photoreduction in H2 to an promoters reduce the activated catalysts, Re2O7/Al2O3, at low temperatures. On adsorption of CO several carbonoxidation state favorable for metathesis and promote foryl-Ni+ complexes were observed. The results obtained with mation of Oz-which stabilize the active sites. Shvets et al. Ni/A1203catalysts appear to be similar to those observed for (027) used ESR to characterize the osmium species derived Ni/Si02 and Ni-CaX systems. Conesa et al. (038) carried from osmium carbonyl clusters supported on cerium oxide and out ESR and NMR studies of hydrogen reduced Rh/Ti02 thorium oxide. In contrast to the low valence ions (Os+ and catalysts. For hydrogen treatments at temperatures less than Os3+)observed on alumina, decomposition of the O S ~ ( C O ) ~ ~573 K, the results indicate not only the formation of H strongly clusters on ceria or thoria resulted in high valence ions (Os bound to the Rh particles but also the reversible generation or Os7+). These osmium ions are proposed to have modified of Ti3+ions and H species weakly adsorbed on the metal. A the redox properties of the respective supports creating new mechanism is proposed implying heterolytic cleaving of Hz centers for 02-formation and localization. at the metal-support interface followed by proton stabilization on the support. The possible role of different forms of H in Corden et al. (028)studied the steric and electronic effects strong metal-support interaction (SMSI)is discussed. Ferino of ligand variation on cobalt dioxygen catalysts. Electronic et al. (039) examined the promoter effects on Rh/Cr203-A1203 and steric factors of Co-dioxygen complexes with systematcatalysts for steam dealkylationof toluene. Based on the ESR ically derivatized pentadentate Schiff base ligands affect their data, it is proposed that coordinativelyunsaturated Cr3+ions ability to catalyze the oxidation of substituted phenols and adsorb Hz and enhance the CO-COz transformation, thus alter the rate of catalyst decomposition. The electronic and avoiding the poisoning of the metal sites by strong CO adsteric factors can be separated sufficiently to indicate that the sorption. activity of the catalyst roughly parallels the trend in the Iwasawa et al. (040) described the preparation and charbasicity of the bound O2 as suggested by ESR hyperfine coupIings of cobalt in the various adducts. Datta et al. (029) acterization of alumina attached chromium dimer and chrostudied the adsorption of sulfur dioxide on alumina catalysts mium monolayer catalysts. These catalysts, active for the by ESR and FTIR spectroscopic methods. Four different hydrogenationof propene at low temperatures, were prepared types of adsorbed species were identified. While the decrease by the reaction between Cr(n-C H5)3and surface hydroxyl in concentration of radicals on heating correlated with the groups of the alumina support folfowed by treatment with H2 disappearanceof IR bands up to 200 "C, the increase in radical Zarrouk et al. (041) examined the direct conversion of isosignal on further heating to 400 "C did not correlate with IR butane into nitriles by interaction with nitric oxide on chrodata. mia/alumina catalysts. Based on the ESR and kinetic data, a redox process is proposed involving Cr3+-Cr5+ions. Ellison Supported Catalysts. Che et al. (030) employed ad(042) discussed the structure of ethylene polymerization sorption of carbon monoxide and third-derivative ESR spectra catalysts. ESR showed different Cr3+resonances indicating (seldom used in ESR) to probe the coordination of surface the prevalence of clustered Cr. At calcination temperatures V4+ions in reduced V205/Si02. Apparently the third derivyielding only partial decomposition of Cr6+,a second p resoative enhances the spectral resolution significantly, indicating nance was observed with evidence for dipole-dipole broadan orthorhombic symmetry for the vanadium ions after CO ening and exchange narrowing associated with chromium adsorption. Further, use of 13C-enrichedCO enabled the clusters. This interpretation sharply rejects the usual model determination of number of ligands to be two. The influences of magnetically isolated crystal field stabilized pentavalent of other adsorbates such as water and ethylene are discussed. chromium ions to be responsible for the observed ESR spectra. Sharma et al. (031) estimated the influence of the carriers McAuliffe and Ashmawy (043) studied with ESR and kinetics on the VO bond strength from the ESR parameters of V4+. the hydrogenation of ethylene over chromia-alumina catalysts. Delocalizationof the vanadium unpaired electron is found to ESR clearly showed that the activity of the catalyst strongly be maximum for the MgO-supported systems. Reduction depends on the presence of Cr3+. Preliminary kinetic studies seems to reduce the VO bond strength on alumina while it showed that the reaction rate is zeroth order in H at -78 "C strengthened it on silica. In similar studies, Simakov and and first order at higher temperatures (>0 "C). Veniaminov (032) examined V MgO catalysts during butylene oxidation. In the absence o f t e olefin, the oxidized catalyst Polymerization Catalysts. Ceausescu et al. (044) indisplayed an ESR signal presumably from tetrahedral V4+, vestigated by ESR the interaction between tungsten hexa-

d

i

76R



b

chloride based catalysts and cycloolefiis. S' als seen in WC after contact with cyclopentene were attri uted to W5+an W3+, the latter being independently confirmed by cerium sulfate titration. The presumed W O was also seen with other cycloolefins, the only variable being the time interval after which the signal developed. During the polymerization of cyclopentane by the WCl,+pichlorohydrin-R& system,three paramagnetic species were seen and assigned to W(V), W(III), and a hydrocarbon radical. The intensity of W3+correlated with the polymerization activity while that of the hydrocarbon radical was related to catalyst deactivation. Sergeev et al. (045) studied ESR of Ti3+in propene polymerization catalysts. Introduction of ethyl benzoate resulted in a significant increase of ESR observable Ti3+along with the increase in stereospecificity and several new resonances. It also resulted in an increase in the amount of Ti in the solution removed from the solid catalyst during the interaction with the or anoaluminum cocatalyst. The active centers appeared to f e localized in highly dispersed particle or surface aggregates of TiC13 formed on the MgC12 surfaces and seen in ESR. Increase in stereospecificity was assumed to be due to poisoning of nonstereospecific active centers by the ethyl benzoate. Skupinski et al. (046) examined the carrier influence on the paramagnetic and catalytic properties of supported titanium complexes. In the Ti complexes prepared by treating aluminadica gels with CpTiC13and excess BuLi, the basicity of the gel seemed to affect the amount of Ti4+and Ti3+complexes on the surface. It is also shown to have significant effect on the symmetry of the Ti3+surface complexes, their electron distribution, and the overall catalytic activity in olefin hydro enation. Yatsenko et al. (047)described the ESR study of t t e interaction of components of a catalyst system such as TiC1,-acetophenone-R3Al as a function of their relative concentration. Six types of bi- and trinuclear paramagnetic Ti3+centers form in the system and they exist as monomeric or associated species. The Ti3+ complexes containing PhCOMe were found to be more stable than the ones which do not have such electron donor ligands. Poluboyarov et al. (048concluded ) from their ESR studies of Ti-Mg Zeigler type catalysts after that interaction with organoaluminum cocatalysts the Ti3+ions formed are mainly as TiCl,-associated species, with some of the Ti being in the divalent state. These could be oxidized to ESR-active Ti3+ after treatment with water and were found to exhibit cooperative Jahn-Teller interactions. Wilson and Smith (049) carried out ESR of divalent Ti ions doped into a MgC12lattice by crystal growth from melt. The ESR resonances were assigned to a forbidden M,= 2 double quantum transition with trigonally distorted octahedral environment around the Ti2+ ions. This information was used to interpret the spectra seen for the polymerization catalyst (powder of such melt grown material R3Al) and compared with ESR observed in a typical catalyst of TiC14 + MgClz + Et3A1. Ito et al. (050) studied the oxidative dimerization of methane over a lithium-promoted magnesium oxide catalyst. ESR, temperature dependence for Cz selectivity, and wei ht dependence of lithium in these catalysts indicated that LigOcenters are responsible for abstracting an H atom from methane in the initial step in partial autooxidation to ethane and ethylene; CO and C02me byproducts. The Li+O- exists in an equilibrium state at high temperatures (- 100 "C) in the presence of 02. The autooxidation kinetics show that methyl radical is the common reaction intermediate in the formation of C2compounds. Below 700 "C CO and C 0 2are formed which react with the surface 0; or O2 gas resulting in chain reactions and formation of more methyl radical. Poluboyarov et al. (051) examined the peculiarities of ethylene interaction with surface alkyl compounds of Ti3+in ethylene polymerization catalysts prepared via the reaction between tetrabenzyltitanium and silica. Fiero et al. (052) characterized silica-su ported uranium molybdenum oxide catalysts by ESR, IR, XP8, and X-ray diffraction. A mechanism for the promotional effects of uranium on this butene oxidation catalvst is proposed. HDS and HDN Catalysts. Thakur and Delmon (053) examined bv ESR the role of g r o w VI11 Dromoters in molybdenum disulfide and tungken-disulf(de hydrotreating catalysts specifically in two ranges of promoter concentrations. In the low as well as the high limits, trivalent Mo or W were

7

+

detected. For low romoter concentrations the ESR signal due to defects in t t e host disulfides was found to be suppressed while for high concentrationsa ferromagnetic behavior was observed. Stronger electronic interaction with the promoter is indicated in the WS2 catalysts. Kohno et al. (054) described high-temperature and high-pressure ESR studies of Mo reduction in supported Mo catalysts. The support material was found to have a strong influence on the reduction behavior of the catalysts a t high temperatures under a high pressure of H2. The ease of reduction decreases in the order Mo03/Sn02> Moo3 Zr02 > Mo03/Ti02> Mo03/A1203> Mo03/Si02> MOO,/ go. Completely opposite trends were seen in electron transfer reactions with 9-methylanthracene for Mo03/A1203and Mo03/Zr02indicating the importance of support properties. The interactions of Mo5+ on Mo/Si02 were studied on catalysts (055) prepared by impregnation and hydrogen reduction at high temperature. ESR and ESEM analysis techniques were used. Two types of Mo(V) were seen, one of them being sensitive to adsorption of small molecules like MeOH, NH3, etc. This species is suggested to be in five coordination on the surface of thesupport. In related studies Zhan et al. (056) suggested that both of these species are insensitive to oxygen adsorption and that there is yet another Mo species very sensitive to O2adsorption, immediately resulting in the superoxide 02-formation. If polar adsorbates such as water, methanol, or ammonia were adsorbed prior to oxygen adsorption, superoxide formation was inhibited. Nonpolar adsorbates such as ethylene or MeCN do not seem to compete with O2as subsequent adsorption of oxygen results in the formation of the oxygen radical. The Mo species sensitive to 0; formation is suggested to be either Mo5+or Mo4+ ions in symmetric tetrahedral environments, thus precluding their ESR observation prior to oxygen adsorption. The hydrodesulfurizing activity of Y zeolites modified with CO, Ni, Mo, Zn, and Cu was studied by Davidova et al. (057). ESR was used to follow the changes in the oxidation states of these metals in the oxidized, reduced, and sulfided forms of the catalyst. Sulfidization was shown to reduce the Mo(V) content. Using the model reaction of hydrogenolysis of diethylsulfide, these authors argued that (a) reduction of Mo(V) in the presence of Co is due to formation of Co-Mo-oxy sulfides and (b) either Co or Ni on CaY zeolite has comparable activity to the catalysts containing Mo. Stuart et al. (058) reported an ESR study of zeolite-supported ruthenium hydrodenitrogenationcatalyst. The catalyst prepared by ion exchange with hexammineruthenium tribromide and sullided in a stream of H2-H2S or H2-CS2 showed comparable catalytic activity in conversion of quinoline with reference to a commercial catalyst. Based on the ESR data they postulate that in the ruthenium catalyst the active species is probably a sulfido species of Ru(I1) present along with some isolated binuclear Ru(II1) species in the zeolite. Fricke and Oehlmann (059) studied the ESR of free and supported 12heteropoly acids (HPA) of Mo. They concluded that the stability of supported HPA is markedly dependent on the nature of support and that it is necessary for the Keggin structure to be destroyed to facilitate the formation of 02radicals upon oxygen adsorption. The pathways for the formation of the different Mo5+ are discussed. Derouane et al. (060) investigated by ESR the paramagnetic species present in unsupported and supported Co-Mo (Co Mo = Ck2.3) Catalysts. Three distinct species were observed: L O , MS, and CMS. MO correspondsto oxo-Mo5+ions interacting with the alumina support while MS is either a defect in bulk MoS2 phase or a thio-Mo5+ species located on the edges of the layered MoS2 crystallites. Addition of Co decreases the intensities of both these species simultaneously generating CMS. Its intensity ra idly increases with cobalt content reaching a maximum at 8o/Mo = 1. The intensity of the CMS signal parallels the HDS activity and is proposed to be indicative of special Mo atoms neighboring the Co edge atoms. A two-center model is proposed. Dyrek and Labanowska (061) studied by ESR the interactions of oxygen with Moo3 obtained by thermal decomposition of ammonium paramolybdate. The different accessibilities of the four paramagnetic Mo5+ centers of various symmetry and of the Mo3+centers to oxygen are explained in terms of their location (surface versus bulk) and the method of stabilization. A mechanism is given for transformation of

k


77 R


Mo ions into diamagnetic Mo(V1) species. Che and Louis ( 0 6 2 ) described the formation of 0-on reduced Mo/SiOz catalysts prepared by grafting. The 0-formed by adsorption of NzO is favored by the presence of tetracoordinated MOW) species which are characteristic of the rafted catalysts but seldom seen on impregnated catalysts. #hese oxygen radicals were found to be stale at room temperature and experimental conditions are proposed to obtain optimum concentrations of 0-.The intensity of 0-radicals could thus be used as a direct indicator of the tetrahedral Mo content. Reddy et al. (063) studied ESR, oxygen chemisorption,and HDS as well as the hydrogenation activity of Mo03/ZrOz catalysts. The results are explained on the basis of a patch model of the Mo oxide phase. Guglielminotti and Giamello ( 0 6 4 ) characterized a Mo/SiOz system by ESR, UV-Vis, and IR. The catalyst was prepared by molybdate impregnation or MO(CO)~ heterogenation and reduced at 823 K with hydrogen. Photoreduction in a CO atmosphere leads to further reduction of Mo. A s cies involving two Mo(I1) ions bridged together through a C r i s postulated. This species is suggested to be in equilibrium with a distorted Mo(I1) ion attached linearly to two Co molecules. Mitchell and Scott (065)discussed the interaction of vanadium and nickel porphyrins as well as metal-freeporphyrins with Mo-based hydroprocessing catalysts. The binding and reactivity of the porphyrins on oxide and sulfide surfaces are described. It is suggested that the porphyrin ring is oxidized, a t a meso-C by oxomolybdenum species and adsorbed 0, to a cation radical and an oxophlorin. During HDS, porphyrin bound to the catalyst is hydrogenated at the meso-C to phlorin. The relevance of these results to catalyst deactivation is discussed. Johnston et al. ( 0 6 6 ) characterized the active sites on molybdenum disulfide HDS catalysts by complementary magnetic susceptibility and ESR techniques to check the hypothesis that all the sites seen by O2chemisorption are probably magnetic, only a small fraction of them being detectable by X-band ESR. While a large difference was indeed noticed between the susceptibility and ESR numbers, both of them increasing monotonically with the rate of HDS of dibenzothiophene,the origin of the disparity was not resolved. However, the susceptibility and oxygen chemisorption measurements were in quantitative agreement. Nonroutine Studies. Vogt et al. ( 0 6 7 ) studied the properties of metallic nickel in reduced Ni-NaY zeolites. The degree of reduction was measured by temperature-programmed reduction with H and the dispersion of Ni was characterized by 0 chemisorption. Ferromagnetic resonance (FMR) was used to measure the d-electron density of Ni species. &si et al. ( 0 6 8 ) examined Cu-Cr oxide catalysts which have spinel structure. By comparison of XPS and ESR data changes in Cr3+ line width and susceptibility data were correlated to changes in concentration of Cu+. These octahedral Cu' ions are suggested to have an active role in the selective hydrogenation catalysis. Beringhelli et al. ( 0 6 9 ) examined the paramagnetic metal species on highly dispersed rhodium/ polyphosphine catalysts. Magnetically dilute Rh(0) centers were observed at high P/Rh ratios. Two different Rh(0) species were seen with their relative amounts dependent on the P / R h ratio. The resonance shape was found to depend on the metal particle size as well as the absolute Rh percentage. Flockhart and Salem ( 0 7 0 ) studied the interaction of perylene with alumina surfaces in order to characterize the acid sites. ESR spectra of perylene on alumina become less resolved with time. The decay rate of resolution is dependent on the concentration of the adsorbed radical and to a lesser extent on the activation temperature of the catalyst. Radical concentrations10 88R

0

ANALYTICAL CHEMISTRY, VOL. 59,

NO. 12, JUNE 15, 1987

kcal/mol). This problem limits the utility of TPD methods for quantitative acid site distribution determinations and, perhaps, for good activity correlations. As a result of catalytic activity studies, the high-temperature peak (about 300 to 500 "C) in the TPD of ammonia was often linked to strong Bronsted acid sites. Correlations were observed with hydrocarbon cracking activity in a variety of modified zeolites (17-19). The same strong acid TPD peak was also correlated with catalytic activity in the transformation of methanol into hydrocarbons over ZSM-5 (110-112), in the alkylation and isomerization of aromatics over ZSM-5 (113, 114),in coke formation in ZSM-5 (11.9,in butane oxidation over vanadyl pyrophosphate (116), and in synthesis gas reactions over hybrid Pd/SiO,/zeolites (117). The strong Bronsted character of the high-temperature chemisorption site was inferred in a number of cases by solid-state NMR (118, 119, 18, 19) and infrared spectroscopy (118, 120, 121, 131). However, it is still uncertain whether high-temperature ammonia chemisorption is associated with dehydroxylated sites, strong Bronsted acid sites, and/or Lewis acid sites (131). Perhaps it depends upon the nature of the specific catalyst. Correlations between "total" chemisorbed ammonia and the acidic catalytic character of modified y-alumina (122) and amorphous silica alumina (123) were also reported. However, no unique type of acid site was identified with activity in those studies. Correlations of "total" chemisorbed ammonia with activity appear quantitative mainly in situations where strong Bronsted acidity was reported responsible for activity and where, in addition, the analyst has taken considerable precaution to eliminate physisorbed ammonia. In a somewhat different type of application, Moffat (124) employed TPD of water, ammonia, and pyridine chemisorption in conjunction with infrared photoacoustic spectroscopy to characterize proton acid sites in the heteropoly solid acid catalyst, 12tungstophosphoric acid. Temperature-programmed reduction (TPR) and temperature-programmed isotopic exchange (TPE) of H2,HD, and D2were also used in order to characterize the reactivity of acid sites. In this particular case, significant differences were observed between the sorptive behavior of ammonia and pyridine. At the appropriate temperature (Le., 150 "C), stepwise ammonia adsorption gave the expected stoichiometry of 3 (i.e., H3PWI2O4,-J. Pyridine adsorption, however, was found to have a slow and fast phase. The type of pyridine binding which occurred, as determined via infrared, was found to be dependent on the concentration (i.e., stoichiometry) of pyridine used during adsorption and the thermal history of the sample (i.e., degree of hydration of the catalyst). It was concluded that hydrogen-bonded water blocked access to pyridine, but not ammonia. TPE profiles (i.e., D,, HD, and H2)confirmed the presence of active hydrogens and provided further information enabling the interpretation of TPD and TPR data. Alternate Base Sorbents. In an attempt to find alternate bases for TPD studies, Parker et al. (125) evaluated the use of ammonia, pyridine, and a series of primary amines for ZSM-5 characterization. Using TPD/MS, they concluded that primary amines were not useful for TPD studies due to reactions forming dialkylamines and decomposition to alkenes and ammonia. Morishige, Kittaka, and Ihara (126) characterized the sorption behavior of methylamines on NaX, Nay, and KY zeolites. Isosteric heats of sorption were determined and sorption sites were postulated. Corma et al. (127,128) reported on the use of the stronger base, 2,6-dimethylpyridine, for the identification of weaker Bronsted acid sites on yalumina and fluorinated y-alumina. Busca et al. (129) employed TPD of methanol and FTIR to probe the acid-base properties of TiO, and KOH-doped TiOz. Using FTIR and the energetics information from TPD, they suggested five modes of surface interactions for methanol with acid and base sites. For a bifunctional catalyst, Ti02-Zr0,, Wu et al. (130) used the sorption of both n-butylamine and acetic acid to quantify acid and base sites and correlated these with ethylene dehydrogenation and catalyst poisoning. Microcalorimetry. Microcalorimetric studies of ammonia adsorption were also successfully applied for the characterization of acid sites. Again, most applications were with strong acid catalysts, mainly zeolites. As in ammonia TPD, two or three distributions of acid sites were typically differentiated based on changes in differential heats of adsorption (120, 132-138). Differential heats of adsorption usually fell in the


ranges >140,76140, and C 70 kJ/mol. Calorimetric data were correlated with cracking activity (120,133,134),alkylaromatic isomerization and disproportionation (132,134,138), dealumination (132,133, decationization (136,138), fluoridation (133),and high-temperature dehydroxylation (135).Infrared spectroscopy was also used in conjunction with calorimetry to identify calorimetrically distinguishablesites (120,137,138). Auroux and Vedrine (139) employed microcalorimetryfor the characterization of acid and base sites of various metallic oxides and zeolites (MgO, S O z , SiOz-AlZO3,A1203,Bi3FeMo2012,TiOz, and Y- and ZSM-5 zeolites). In that study, correlations were found in a situation where catalytic properties involved both acid and base sites with electron donor and acceptor properties. Ammonia and carbon dioxide were selected as sorbents in order to avoid diffusion limitations. Yushin and comrades (140)determined the heats of sorption of H2 and CO on Zn/Cr and its KzO-promoted catalysts. A dramatic increase in CO sorption energy (from about 90 to 300 kJ/mol) was observed with promoter. It was suggested that this increased adsorption energy was related to the increased selectivity of promoted catalysts for Cz-C4 alcohols. Solution Titrations. New variations on acid-base titrations of catalysts suspended in nonaqueous media continue to be developed. However, these techniques do not appear to be as widely used as gas-phase adsorption. Techniques were principally developed for acid site distribution determinations. Cid and Pecchi (141) proposed a glass electrode potentiometric method employing n-butylamine as titrant in acetonitrile. They characterized the acid site distribution of NH4-NaY zeolite, A1203,and SiOZ-AlzO3and demonstrated good correlation with results from the Benesi method. Acid distribution results were also presented for various oxides of the Mo-Fe-Te-0 system. Hashimoto et al. (142,143)presented a new approach for measuring acid strength distribution via the determination of the Langmuir isotherms for a series of Hammett indicators adsorbed onto catalyst. Adsorption was followed by UV-Vis spectroscopy in cyclohexane or benzene as solvent. The acid distribution curves of a series of silicaalumina catalysts were measured over the range -15 < H,C -3. Overall reaction rates for cracking cumene over silicaalumina catalysts were estimated by using the experimental data and good correlations of overall rate with distribution of acid sites were observed (143). In a similar manner, Homs et al. (144,145)used the Langmuir behavior of the base titrants quinoline, pyridine, and cyclohexylamine (i.e., in cyclohexane solvent) to characterize the acidity of supported iron catalyst on y-alumina. Sinisterra et al. (146) used an analogous approach, but with UV derivative spectroscopy, for the characterization of base sites on low surface area barium hydroxide. In that case acidic indicator titrants were used. Molodozhenyuk and co-workers (147) employed a large series of acid-base indicators with pK, from -5 to +26, in conjunction with UV-Vis diffuse reflectance spectroscopy, to determine the site distribution for a series of oxide catalyst carriers (Le, based on aluminum, magnesium, and calcium). With some indicators, shifts in absorption bands were related to Bronsted or Lewis acidity. Shifts in the visible spectral characteristics of p-dimethylaminoazobenzenewere also reported to characterize acid centers in modified kaolinites (148,149). Anderson and Klinowski (150) review the applicability and limitations of employing Hammett indicators for the study of zeolite catalysts. The authors concluded that the popular belief that Hammett indicators do not enter zeolitic cavities for steric reasons is not always justified. Also, some indicators are not appropriate for zeolites with high framework aluminum content. An experimental procedure was proposed for determining the concentration and strength of acid$sites in zeolites. Model Reactions. Probably the most direct approach for quantifying surface acidity related to catalytic activity is still through the use of model reactions. However, this approach is often complicated and tedious. Guisnet (151) recently reviewed the philosophy for acid site characterization via hydrocarbon conversion reactions. Corma and Fornes (152) presented an approach for using the cracking of alkanes as test reactions for solid acid catalysts. The methodology avoids the difficulties resulting from catalyst decay and secondary reactions. Fornes related the protolytic-to-18 cracking (P/P) activity ratios of n-he tane to the “active” Bronsted/Lewis ratio of zeolites. In a 8fferent application, Fajula et al. (153)

correlated the activity of alcohol yield per protonic site with the aluminum content of zeolite catalysts. The correlation existed regardless of the zeolite framework structure. The hydration of n-butene over mordenite, ZSM-5, offretite, omega, and Y zeolites were evaluated to demonstrate the correlation. Giordano et al. (154) were able to show a linear relationship between the disproportionation-isomerization of rn-xylene over a series of dealuminated mordenites to intermediate electronegativity and hydrogen charge, or proton activity. A critical review by them of earlier work showed the existence of the same relationship for a variety of zeolites over a range of 6 orders of magnitude in reaction rate. Davis (155) proposed a model in which alcohol dehydration selectivity (i.e., for secondary alcohols) could be used as a measure of the base strength of metal oxide catalysts. It was proposed that in cases where 1-and cis-2-alkenesare the most predominant products, steric effects are imposed by the catalytic site. Whereas, in the case where almost equal amounts of cis- and trans-2 isomers are formed, the amount of 1-alkene produced could be used as a relative measure of base strength. For zeolites, Karge, Kosters, and Wada (156)used the dehydration of cyclohexanol as a test reaction for acidity in mordenite, clinoptilolite, and faujasite Y zeolites. Nagy et al. (157) characterized the reactions of [2-13C]-2-propanolon K- and Csexchanged ZSM-5 and mordenite in order to deduce both acid and base site information. Kinetic measurements were coupled with 13C,lH, %i, and nAl solid-state NMR. In the case of hydrocracking, Beyerlein et al. (158)were able to correlate carbonium ion selectivities with acidity and framework A1 content for a series of dealuminated and sodium-poisoned ultrastable Y zeolites. Free Metal Surface Area. Scholten, Pijpers, and Hustings (159) provided a fundamental review of surface characterization of supported and nonsupported heterogeneous hydrogenation catalysts. They concentrated their review on free-metal surface area determination via hydrogen and carbon monoxide chemisorption and temperature-programmed desorption of hydrogen. In-depth and critical discussions of fundamental characterization principles were presented. Specific review sections were dedicated to Cu, Rh, Pt, Pd, Ni, and Ru. Some fundamental applications of Auger and XPS, as related to catalyst poisoning, were also covered. The authors feel that there are good fundamental reasons to select hydrogen for surface area or dispersion measurements instead of carbon monoxide. However, there are situations where the adsorption of carbon monoxide in the presence of an excess of hydrogen has special advantages. Wells and co-workers of the European Group on Catalysis presented the results of their 20 laboratory collaborative study on a reference standard platinum/silica catalyst, “EUROPT-1” in a series of five papers (160-164). Platinum dispersion was characterized by Hz, CO, and O2chemisorption using volumetric, gravimetric, frontal chromatographic, and pulse chromatographic techniques. The chemisorption data were interpreted with the aid of N2 sorption characterization, mercury porosimetry, elemental analysis, XPS, EXAFS, TEM, proton NMR, and IR. The estimation of platinum surface area based purely on chemisorption data proved difficult. The forms of the chemisorption isotherms were such that conditions for full surface coverage could not be defined clearly. Electron microscopic data were required to infer chemisorption stoichiometry. However, the study proved highly successful with the insights achieved and the generation of a highly acceptable reference material. Good agreement was found between the variety of chemisorption methods used. Martin, Pajares, and Tejuca presented an example of what can often happen when a variety of methods are compared for a given problem. They performed a comparative study of chemisorption methods (H2,CO, O2 chemisorption, H2-02 and 02-H2 titrations) for Pd surface area of Pd supported on Alz03 (165), sepiolite and A1P04 (166), and on carbon black and sulfonic resins (167).Chemisorption data were supported by TEM, XRD, and IR. Different methods were found to be optimum for different supports. In the case of alumina and carbon supports, H2chemisorption under controlled conditions (i.e,, 343 K and 6 2 0 torr) was the most accurate. On sepiolite and AlPO, all methods were considered reliable exceDt CO chemisorption and TEM, which gave results about 20% high. For Pd/resin. O,-H, and H,-O,, TEM and XRD yielded consistknt res’ulti fo; catalysi o f k e t a l particle size greater ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNE 15, 1987

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than 40 A. Particle sizes determined by CO adsorption deviated significantly from the results of the other methods. Blik, Vriens, and Prins (168,169)studied the time dependence for the room-temperature adsorption of Hz and O2 on Rh/ rutile and Rh/anatase. H2 spillover resulting from metal support interactions and O2 metal oxidation were suggested as slow phase interferences. In order to overcome effects resulting from metal-metal interactions, Shastri and Schwank (170,171) developed a stepwise chemisorption and surface titration technique using Hzand 02. In the method, the temperature of titration is adjusted to optimize specific metal sorbent interactions. Wang, Lercher, and Haller (172)reported an interesting example of the effects of impurities on the determination of Rh on MgO supports. When 98% and 99.5% pure MgO support materials were used, they observed, respectively, a 3- or 20-fold decrease in H2 chemisorption capacity and a 3 or 5 orders of magnitude suppression of ethane hydrogenolysis activity when comparing high-temperature reduction (773 K) to low-temperature reduction (523 K). When 99.999% pure MgO was used for the support, no effects were observed. Parris and Klier (173)reported the determination of specific copper surface area on Cu/ZnO methanol synthesis catalyst via O2 and CO chemisorption. When compared, reversible CO capacities (293 K) had a good linear correlation with irreversible O2 (78 K) capacities. A critical comparison of the method with the traditional N 2 0 decomposition procedure indicated that low-temperature O2 chemisorption is preferred for the determination of crystalline copper surface areas. In an interesting application, Blackmond and KO (174) probed the surface structure of a series of Ni/SiOz catalysts by CO adsorption and H2 CO coadsorption using quantitative chemisorption and I spectroscopy. These techniques were found to be sensitive probes for surface smoothness in terms of the presence of defect sites and surface structure in terms of the types of planes exposed. Temperature-Programmed Sorption Techniques. Temperature-programmed methods are popular because they are simple and convenient and can present a wealth of data, even in complex matrices. However, disadvantages include the fact that the dynamic sorption/desorption processes taking place can be very complex. Quantification may also turn out to be unreliable unless independent calibrations are carried out. Theory. Richards and Rees (175)presented a new method of analyzing TPD curves measured at different heating rates. The activation energy for desorption, preexponential factor, and isosteric heats of adsorption were evaluated at constant coverage via a mathematical minimization technique. The method was demonstrated for the TPD of ethanol, n-hexane, n-octane, and p-xylene on ZSM-5/silicalite. Good agreement was obtained when results were compared to calorimetric and isosteric data. Ehrhardt e t al. (176) developed a general mathematical model for analyzing TPR data for the estimation of kinetic parameters in the case of several overlapping single steps. The computer simulation method included the mathematical deconvolution of incompletely resolved individual peaks. Application was demonstrated for Cr03/Si02catalyst. Sermon and co-workers (177) presented a provocative paper and discussion concerning temperature-programmed methods of analysis. Their purpose in presenting the work was to test the validity of TPR and TPD to oxide-supported platinum and its precursor chlorometallic acid. They pointed out the inherent dangers of the a priori assumption that distinct temperature programmed profiles (i.e., the temperature-dependent fingerprint) can be interpreted in terms of processes occurring on chemically distinct and distinguishable solid or surface states. They also pointed out that the activation energy for diffusion is critically important and in some cases diffusion may be too slow in T P R and too high in TPD to allow temperature-programmed profiles to arise from processes occurring from distinguishable and identifiable species. TPD surface residence times are also important in defining the fraction of adsorbate subsequently desorbed. The paper then reported an in-depth analysis of experimental data for Pt unsupported and supported on silica, alumina, and titania. Apparent quantification discrepancies and support-dependent temperature profiles were also discussed. Babenkova and comrades (1101) reported on a systematic study of hydrogen desorption from carbon blacks using TPD.

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They reported that the bond energy of both molecular and atomic forms of hydrogen increased with the complexity of the d-electron structure in triads of group VI11 metals, in agreement with theoretical calculations. Thus, activation energies for desorption behaved in a predictable periodic manner. Sanchez-Burgos et al. (1102) were able to demonstrate by TPD-GC that the statistical BET model of Oh and Kim for the determination of the distribution of sites on heterogeneous surfaces could accurately model the sorption behavior of N2 and C02 on Yb203. Integration of two CO desorption peaks from TPD-GC resulted in quantification that was in accord with volumetric sorption data. Interpretation. The complexity and pitfalls for interpretation of temperature-programmed sorption data were exemplified by studies related to phenomena such as hydrogen spillover, metal-metal interactions, and strong metal-support interactions (SMSI). An excellent example of typical problems and the complexity of experimental approaches was provided by Maire and co-workers (178). They employed multiple chemisorption techniques using TPR, O2 and H2 chemisorption, 02-H2 titrations, and CO adsorption, as well as H, TPD to characterize the chemisorption behavior of Pt-Ru/alumina bimetallic catalysts. Formation of Pt and Ru bimetallic particles was inferred from TPR and hydrogen titrations. TPD data, however, could only be interpreted qualitatively, not quantitatively, but had distinctive profiles for Pt, Ru, and Pt-Ru. CO and O2 titrations were used to quantify surface Pt and Ru, respectively. However, 02-H2 titration stoichiometry was found to vary with metal proportions. This was interpreted in conjunction with TPD characteristics to reflect changes in Pt-Ru sorption stoichiometry. On the other hand, they found that catalytic activity for the formation of hydrocarbon could directly be correlated with surface Ru. These results were also used for interpretations related to changes in activity with metal composition. Lieske and Voelter (179) studied the state of Sn in Pt-Sn/A120, by TPR and pulse hydrogen and oxygen titrations. They used (a) TPR to follow and quantify the redox states of Sn, (b) hydrogen chemisorption suppression to gauge Pt-Sn alloying, and (c) oxygen chemisorption to quantify the sum of unoxidized Pt(0) and Sn(0). They were able to quantify the presence of the various redox states and conclude the presence and stabilization of Sn(I1) via interaction with the alumina support. Hydrogen Spillouer. Mieville (180) used TPR to study Pt-Re interactions of Pt-Re/A1203 catalyst. Significant shifts in TPR peaks were found with variations in preoxidation temperature and were attributed to changes in Re redox states. H2 spillover from Pt was suggested as the most plausible mechanism for Re reduction during TPR. Goodman and Peden (181) gave examples of quantitative errors resulting from H2 TPD over bimetallic catalysts where “hydrogen spillover” was suggested as taking place from Ru to Cu. TPD peaks showed excess hydrogen sorption for Cu/Ru catalyst system when sample prereduction was performed at higher temperatures (230 vs. 100 “C). Chang, Chen, and Yeh (182) used a combination of TPR and temperature-resolved sorption (TRS) in order to study strong metal-support interactions in supported palladium catalysts. The extents of hydrogen spillover, sintering, and SMSI were found to be support dependent and could be correlated to TPR spectra (i.e., or pretreatment). The adsorption of hydrogen into bulk Pd was suppressed by SMSI. Metal Rearrangement. Prins and co-workers published a series of three reports using TPR, TPD, and TPO (temperature-programmed oxidation) in a systematic and exhaustive study of Co-Rh/A1203, Co/Ti02 and Co-Rh/TiO, and CoRh/Si02 catalyst systems (183-185). TPR and TPO investigations were also supported by H2 chemisorption, ferroma netic resonance spectra, TEM, and EXAFS. TPR, TPD, ancf TPO characteristics for the metals of concern were calibrated against a series of Co and Rh alloys and bulk oxides. Significant variations in oxidation and reduction profiles enabled the authors to formulate models for the formation of bimetallic Co-Rh particles during reduction of the impregnated catalysts. TPR, TPD, and TPO profiles proved sensitive tools for observing temperature-dependent phenomena such as restructbring, alloying, metal segregation, and strong metal-support interaction. They concluded that the general aspects of the TPR and TPO profiles of Co, Rh, and Co-Rh catalysts did not depend much on the support mate-


rials. Generally, during reduction of a coimpre nated bimetallic catalyst alloying of the two metals takes p ace. Once noble metal particles have been formed, they serve as catal$ta in the reduction of the salt of the less noble metal. Paryjczak, Farbotko, and Goralski (186) used a combination of TPR, Hz and O2 chemisorption, and H2-02 pulse titration to evaluate catalyst. The results the surface composition of Pd-Ni A1203 indicated surface enrichment o Pd. They concluded that H2-02pulse titrations were useful for evaluating Pd dispersion, whereas TPR could be used to determine surface Ni. Promotion. Van Den Berg and co-workers (187)employed TPR, and a host of supporting techniques (electron microscopy, elemental analysis, X-ray fluorescence, CO/Hz reaction, ethane hydrogenolysis,pyrolysis combustion mass spectrometry, infrared spectroscopy), to study the effects of Mn and Mo promoters on silica-supported rhodium catalysts. The TPR peak of the promoted catalyst (i.e., reduction of rhodium oxide) shifted to significantly higher temperature when compared to unpromoted catalyst. CO chemisorption was also reduced. These observationswere explained as resulting from a stabilization of Rh+ by surface patches of mixed oxides of promoter manganese and molybdenum. Similar synergistic metal-metal, promoter, support effeds, and spillover affecting TPD sorption spectra have also been CO and reported for CO and H2 on Cu-Rh(ll1) (188,189), Hz on Ni/Ti02 (190-192),CO and Dz on Ni (193),NO on Rh/Ti02 (194).Examples where TPD has provided mechanistic insight because of significant interaction, or reaction, of reactants with catalyst under simulated reaction conditions include H2 desorption from Cu ZnO methanol synthesis catalyst (I%), CO desorption from u Alz03 oxidation catalyst (196),hydrogen desorption from Ru/Y zeolite CO hydro enation catalyst (197),hydrocarbon desorption from molyldemethanol desorption denum oxide cracking catalyst (198), composition from ZnO (199), and oxygen desorption rom mixed metal oxide hydrocarbon oxidation catalysts (1100). Tang et al. (1103)reported on the TPD and TPR of y-alumina up to 1000 "C, presenting new evidence for the reducibility of alumina, together with an inhibition effect for hydrogen chemisorption by alumina, after reduction a t high temperatures. Emphasis was on the evaluation of the support after chlorination and more severe precalcination. These conditions were of particular interest for the study of metal-support interactions. Instrumentation. Serrano and Carberry (1104)described a multifunctional apparatus to permit in situ studies of catalyst samples under controlled atmospheres. Several useful catalyst characterization techniques were integrated into one apparatus. These included gas pulse chemisorption and titration, TPD, TPR, and a recirculation gradientless reactor for reaction kinetics evaluation. The recirculation reactor was demonstrated by studying CO oxidation over Pt-Rely-alumina. H2-Oztitrations and TPR were demonstrated by using the same catalyst. TPD was demonstrated via the desorption of water from y-alumina. Arnoldy et al. (1105)described a flow system for studying sulfiding via temperature-programmed sulfiding (TPS). The apparatus was used to characterize sulfiding patterns of the hydroprocessing catalyst, Moos/ AlzO,. In the TPS studies HzS, HzO, and Hz concentrations were measured continuously as a function of temperature, while sulfiding with a H2S/Hz/Ar mixture. TPS appeared to be a sensitive technique for studying sulfiding phenomenon and, combined with TPD, TPR, and spectrosco ic techniques, could provide considerable insight on sulfi8ng rates and mechanisms. In TPS, both H2S adsorption and desorption are followed as a function of temperature and are interpreted as resulting from HzS sorption or reaction processes (Le., sulfiding). Thus reactions must be postulated, or determined. TPS profiles were shown to be considerably influenced by catalyst composition and pretreatment (i.e., water content, prereduction conditions, and molybdenum content). The TPS data lead to considerable postulation concerning the mechanism of sulfiding. Brito and Laine (1106)also used TPR to characterize molybdenum catalysts. TPR spectra changed significantly with molybdenum content, type of support, calcination temperature, and the type and amount of promoter. In another study by Daly, Schmitt, and Stern (1103, TPD analysis of chemisorbed NO suggested that the reactivity of Mo sites for the disproportionation of NO to N 2 0 could be related to molybdenum support interaction.

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In a unique approach for the study of H2 chemisorption, Goodwin et al. (1108)applied the technique of frequency response chemisorption (FRC). This volume modulation technique identifies reversible adsorption-desorptionprocesses taking place in the 0.01-100-9 time regime. They chose to examine the anomalous chemisorption behavior of H2 known to result from high temperature treatment of titania-supported rhodium catalysts. The suppression of strong H2 chemisorption on these catalysts has been ascribed to strong metal-support interaction (SMSI). SMSI-Rh/Ti02, normal Rh/TiOz, and normal Rh/SiOz were studied. A comparison was also made between the static, volumetric Hzchemisorption of these catalysts and their FRC behavior. The comparison of FRC spectra between Rh/Si02 and Rh/Ti02 showed a clear distinction. On the contrary, the total static Hzchemisorptive behavior of these two catalysts was very similar. Surprisingly, little difference was observed between normal and SMSIRh/TiOz. For all catalysts, at least three kinetically distinct modes of H2 chemisorption were observed. Since FRC only monitors weak chemisorption (i.e., rapid and reversible) occurring on distinct sites, only low-energy H2 adsorption processes were followed. The advantage of the technique is that interferences from strong, irreversible H2 chemisorption processes do not occur. Temperature-dependent FRC spectra for the three Rh catalysts were interpreted as representing the equilibrium of hydrogen states resulting from rapid "molecular" hydrogen adsorption processes (i.e.,. H2(gas) H H2(ads) H(ads)). Chromatographic Techniques. Forni et al. (1109,1110) applied the gas chromatographicpulse method (i.e., with flame ionization detector) for the evaluation of thermodynamic and kinetic parameters relating to the sorption-diffusion of aromatic hydrocarbons in zeolites Y and ZSM-5 at high temperatures (613-713 K). Equations were derived and experimental procedures developed for modeling the various ratedetermining sorption-diffusion processes involved. Main advantages to the method were the simplicity and speed with which considerable comparative data can be obtained. Principal disadvantages were still found to be the complexity of data evaluation and interpretation, and the restricted limits within which experimental parameters are confined. Because of these limitations, no reliable kinetic data could be obtained for mesitylene and only incomplete data were obtained for m- and p-xylenes. Interpretable thermodynamic data were reported for all compounds. However, kinetic parameters were obtained only for benzene, toluene, and o-xylene. Lechert and Schweitzer (1111)used the GC technique as an alternative to conventional gravimetric and volumetric methods for determining the sorption isotherms of butane and 1-butene on a series of ion-exchanged A zeolites. Distinct differences between the two hydrocarbonswere found. These were ascribed as indicative of the dominant role of cations in the sorption processes. The data were also correlated with theoretical model isotherms and isosteric heats of adsorption. Where available, the results agreed well with previous publications and other techniques. Hillerova et al. (I112) successfully applied the GC method for the determination of adsorption isotherms for benzene and heptane on oxidic and presulfided forms of Mo/A1203 and CoMo/A1203catalysts. The presulfided forms adsorbed more than oxidic forms. The differences between the two forms were higher in the case of promoted catalyst. Campelo and co-workers (1113)used GC to determine the adsorption characteristic of a series of alkylaromatic hydrocarbons on AlPO,, A1203,and Si02catalysts. Adsorption heats at low coverage were determined by measuring the retention volumes of adsorbate at different temperatures. Free energy and entropy values were also calculated. The adsorption processes were found to be exothermic. Relative sorption constants were found to fit the Taft-Pavlich equation. Electrical effects were identified as the primary influence in the a-methylated series while steric effects were proposed for the normal series. Rajaram and Sermon (1114)compared the pulsed GC and volumetric H2 chemisorption methods for Co,Feg,O4 spinels. They found reasonable agreement and Langmuir behavior for both methods. An increase in Co content resulted in improvement in the extent and enthalpy of the fast hydrogen adsorption. Hall et al. (1115)used GC to calculate adsorption isotherms and heats of adsorption for the reactants (Le., ethylene, oxygen, hydrogen, chloride) and products (Le., 1,2ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNE 15, 1987

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dichloroethane,ethane, acetylene, propene, 1,3-butadiene,and water) of the oxychlorination of ethylene. These were evaluated for low coverages on CuCl, and CuCl and their alumina-supported catalysts. The unsaturated nature of adsorbates and T bonding were identified as vital factors contributing to significantly higher heats of adsorption. The effects and high heats of adsorption of water were also noted. In a more unusual application, Gishti et al. (1116) employed liquid chromatographywith UV detection to study and control the addition of phosphate, and or heptamolybdate, anions to y-alumina. Frontal analysis proved to be a very efficient diagnostic tool for determining the adsorption capacity of catalyst. Molybdate and phosphate were found to compete for sites and adsorbed in equivalent limiting amounts. As P content increased, the isomerization activity of y-alumina decreased, in parallel with decreased adsorption of Mo(V1). The results were interpreted by hypothesizing the presence of strained Al-0-A1 groups having Lewis acid-base character and adsorption properties. Surface Area and Pore Volume. Zeolites. Sorption techniques for evaluating zeolite characteristics are ever increasing in applications. Because of the relative ease of application and sensitivity, sorption techniques are routinely used for evaluating fundamental zeolite properties such as crystallinity, pore size, pore volume (i.e., sorption capacity), shape selectivity, and thermodynamic properties (i.e., heats and entropies of sorption). Where molecular shape selectivity and adsorption energy are distinct, sorptive behavior can often be correlated with catalytic results. Stach et al. (1117) have recently presented a comprehensivereview on the adsorption equilibrium data for hydrocarbons on highly dealuminated zeolites. A comprehensive review of data is given for the zeolites US-Ex, silicalite, NaX, Nay. They concluded that highly dealuminated zeolites have less energetic heterogeneity with respect to hydrocarbon sorption than do the basic molecular sieves NaX and Nay. An analysis of their thermodynamic properties revealed a strong influence by the diameters of the pore systems on the thermodynamic parameters. Janchen and Stach (1118) reported that with the dealumination of NaX, Nay, and US-Ex, heats of sorption for ndecane decreased. Likewise, Dzhigit and co-workers (1119) reported a decrease in the heats of sorption of propane, cyclohexane, and benzene on Na zeolites of the faujasite type as the number of exchange cations decreased. On the other hand, Ruthven and Goddard (1120) discovered very little difference in the heats of adsorption of C8 aromatic hydrocarbons on Nay, NaX, and KY zeolites at typical Henry’s law pressure regions. A simple statistical model appeared to provide good representation for experimentalequilibrium data. The model correctly predicted an experimental observation of significant interaction between sorbed aromatic hydrocarbons at high loading. They concluded that this interaction lead to the experimentally observed development of selectivity. Hwu and Hightower (1121) reported on the sorption of C4-C, paraffins, cyclohexane, and aromatics into NiZSM-5 type zeolites. From the comparative dynamic and equilibrium adsorption behavior of n-paraffins, isoparaffins, cyclics, and aromatics they concluded that the pore openings for NiZSM-5 had to be less than 6.0 A. Large heats of adsorption of hydrocarbons demonstrated strong interactions between the molecules and the restricted pores in the zeolite. The relative adsorption data indicated that NiZSM-5 has a pore structure very similar to that of NaZSM-5. Occelli et al. (1122) tested the equilibrium sorption of C5--Cl0hydrocarbons on pillared bentonites and showed that the hydrocarbon uptake was similar to that of ZSM-5. However, catalytic differences were significant. Choudhary and Singh (1123)describedsimple and inexpensive liquid pycnometric methods for measuring crystal density, inter- and intracrystalline pore volumes, sorption capacity, and slow diffusion in zeolites. Sorption data for different hydrocarbon liquid sorbates into ZSM-5 were presented. Using the liquid pycnometric techniques, they found the following order for the sorption capacity of HZSM-5 methanol >> n-hexane = benzene > p-x lene > m-xylene = o-xylene > mesitylene. Intracrystalline Jffusion coefficients were also determined for o-xylene, m-xylene, and mesitylene. A few interesting studies were reported with respect to the search for more specific physisorption methods for surface area and pore volume determination. Inomata et al. (1124)reported the development of a benzene-filled micropore method for 92R


measuring the nitrogen BET “external” surface areas. The method was applied to zeolites of low-to-highSi-to-A1ratios (e.g., ZSM-5). Benzene was found most appropriate for ZSM-5, Y zeolite, and mordenite, while the micropore fillers most often used, i.e., water and hexane, were not useful in all cases. On the other hand, Suzuki and co-workers (1125)reported on the use of water, ethane, propane, butane, and 2,2-dimethylpropane as micropore fillers for NaA, CaA, Hmordenite, NaX, and NaY zeolites. In case where nitrogen could diffuse into micropore channels, even though already filled with a fiiing substance, the “external” surface area could still be determined via the amount of nitrogen sorbed rapidly onto the zeolites. Shields and Lowell (1126) developed a method for the determination of ambient temperature adsorption of gases on micro- and mesoporous catalyst materials. Using techniques of helium pycnometry and large sample sizes (i.e., 130 cm3of bulk volume), they were able to measure the adsorption of nitrogen, oxygen, and ton on materials with surface areas ranging from 5 to 370 m /g. The results showed that the quantity of gas adsorbed is a function of the surface area of the adsorbent and the polarizability of the adsorbate. The number of moles of nitrogen adsorbed per gram of sample was also found to be directly proportional to the initial pressure applied to samples. Advantages of the method are that it is simple and requires inexpensive instrumentation and can be performed at ambient temperatures. In another application of helium pycnometry, Shields and Lowell (1127) demonstrated that for small pore materials, i.e., Linde molecular sieves of 4A or less, the commonly employed DeBoer t-plot method seriously underestimated micropore volume. This is due to the inability of nitrogen to enter pores less than 4 A in diameter. They demonstrated that a combination of methods, employing mercury porosimetry and helium pycnometry, could be used to determine true micropore volume. For molecular sieves greater than 4A pore diameter, both approaches were found to give equivalent results. With respect to macroporous catalysts, Lee and co-workers (1128)reported further development of the method of selective physisorption for measuring catalyst surface area. The purpose of the method is to determine the individual surface areas of both catalyst and support. Initial demonstration of the method involved using the thermal desorption of COz from KzC03/carbonblack and Ag/A1203to determine the fractional surface coverage of each component. In the latest demonstration (1128),NzO was used as the sorbate for determining fractional surface areas of Pt on SiO,. Further theoretical and experimental refinements to the method were made in order to make it effective for this case (i.e., where catalyst only covers a small fraction of the surface area). Comparison with H2 chemisorption results indicated that Pt surface areas for both methods were comparable for Pt loadings at 5, 10, and 15%. Dispersed Pt surface areas were approximately0.3 m2/g. The sensitivity of the physisorption method was less than the H, chemisorption method and could not be applied below this surface area. However, a principal advantage of the method is that it has potential application for supported metal base oxide catalysts, for which it was intended. Niwa, Inagaki, and Murakami took a different approach to this problem. They showed that they could determine the “exposed”surface area of selected support materials on supported metal oxide catalysts via benzoate adsorption (1129,1130). A t 523 K benzaldehyde adsorbs preferentially on metal oxide supports to form benzoate. Benzoate is subsequentlydesorbed via reaction with excess ammonia to yield benzonitrile, which is detected in a pulse flow apparatus. Hence, they call the method the benzaldehyde ammonia titration (BAT) method. Method studies indicated that benzoate adsorbed on alumina, titania, and V203,but not on Vz06. Thus, the method could be used to determine the “exposed” alumina, or “exposed” titania, surface area of supported vanadium oxide catalyst. Pieters and Venero (1131) described a novel high-resolution BET apparatus for the determination of surface areas, pore size distributions, and chemisorption isotherms. By using a flow method, they showed detailed structural information not normally obtainable by traditional volumetric methods. The flow instrument’s advantages included extended range (6000 A pores) and high resolution (lo00 points per isotherm). In more of a theoretical light, McEnaney and Masters (1132) presented an excellent critical review in their assessment of adsorption in microporous carbons. The paper discussed the

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formation and f i e structure of microporous carbons and the nature of adsorption in micropores. They reviewed the principal groups of methods used to model adsorption in microporous carbons. These included the t-plot of DeBoer, the a-method of Sing, the Dubinin-Radushkevich equation, the Dubinin-Astakhov equation, and the Stoeckli equations. Experimental factors and data were also discussed. They believed that BET theories had serious limitations when applied to pore-filling situations, as occurs in micropores. Modeling methods derived from the DR equation were better suited and more informative. McEnaney and Masters concluded that there is as yet no satisfactory method for obtaining micropore size distributions from a single adsorption isotherm. Experimentally, Hacskaylo and LeVan (1133) analyzed hydrocarbon equilibrium sorption data on activated carbon using a modified Antoine equation. In their pore-filling model, they modified the traditional vapor pressure equation by letting equation constants depend on loading. Parameters affecting the isosteric heats of adsorption were varied with pore filling. Good correlations with experimental data were observed. In most cases the two-parameter form of the Antoine equation correlated better with experimental data than the three-parameter Dubinin-Radushkevich or Dubinin-Astakhov equations. With respect to molecular sieves, Hope et al. (1134) performed a careful analysis of the adsorption of krypton and to nitrogen on silicalite at 78 K over a pressure range of 1 torr. Results were analyzed in terms of the Hill-deBoer model for homogeneous adsorption and the Langmuir models. The advantage of the Hill-deBoer model was that it allowed for a heterogeneity of adsorption sites. Calculations resulted in energy distributions with several distinct binding sites modeled for the internal surface of silicalite. Calorimetry. Gravelle (1135) recently surveyed the applications of adsorption calorimeters for the measurement of catalytic activities. Applications included the determination of (1) rate laws, (2) probable reaction mechanisms, (3) secondary processes leading to activation and deactivation, and (4) surface site distribution. The merits and limitations of the various applications of adsorption calorimetry for the study of heterogeneously catalyzed. reactions were critically discussed. Because of its sensitivity, and recent developments in refined data-reconstruction techniques, Gravelle suggested that calorimetry was one of the few tools available with which to study the heterogeneity of active sites during catalysis. Often the method is used only to correlate adsorption heat (i.e., bond energy) to catalytic activity or metal dispersion. As reviewed in the sections on surface acidity, ammonia chemisorptionfor acid sites was used successfully on a number of occasions to determine acid site strengths and distributions. On a few occasions unique information was provided by calorimetry for the identification of a specific number of catalyst adsorption processes and their relative abundance. Busca et al. (1136) employed microcalorimetryand Fourier transform infrared spectroscopy to study the states and distribution of methanol on Alz03. The curve for differential adsorption heats plotted as a function of increasing coverage could be resolved into three distinct steps. Infrared data were correlated with the calorimetric data to identify three different forms of methanol binding to A1203: (1) a strong Lewis interaction, (2) a bridged methoxide species, and (3) a reversible hydrogen bonded form. Calorimetric heats were correlated with expected structural bond strengths and aided IR interpretations. Stradella and Vogliolo (1137) used differential adsorption heat curves for assigning species related to the action of bismuth molybdate catalysts. These catalysts are used extensively for the selective oxidation and ammooxidation of unsaturated hydrocarbons. The interactions of the catalyst with water, oxygen, and propene were investigated. Three distinct oxygen interactions, two water interactions, and three propene interactions were identified from calorimetric isotherms. The differential heats for propene interaction with catalyst enabled the assignment of two of these to r-allyl complexes of the olefin (Le., 40 and 30 kJ/mol) and the third to a van der Waals type interaction (i.e., 16 kJ mol). Stradella and Pelizzetti also studied the energetics an thermokinetics of the adsorption of oxygen (1138,1139) and hydrogen (1140) on titanium dioxide. Two types of oxygen interactions were identified in adsorption with RuOz-loaded Ti02 (i.e., doped TiOz), while only one interaction was observed for pure Ti02. Irreversible and reversible characteristics of the calorimetric

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isotherms correlated with volumetric chemisorptionisotherms and Langmuir type behavior. Hydrogen energetics on Rhloaded TiOzwere much more complex, indicating at least three types of interactions. Further work will be required to sort out individual interactions. The thermodynamic data did, however, indicate that the weak reversible interactions for hydrogen (5 kJ/mol) and oxygen (5 kJ/mol) probably result from physical nonspecific adsorption. Whereas, the more energetic irreversible processes for hydrogen (10 kJ/mol) and oxygen (16 kJ/mol) chemisorption probably involve dissociative adsorption. Because of its strong binding energies and infrared characteristics, CO microcalorimetric adsorption studies have also been followed successfully in combination with infrared. Infrared showed that on y-alumina supported Rh, Pt, Pd, and Ir only linear complexes were formed (1141). Formation energies ranged from 3 to 7 kcal/mol. Fubini et al. (1142)found that CO released considerable more heat in adsorption studies on CaO (25 kcal/mol). This value is much higher than that typically found for the simple coordination of CO onto surface acidic sites. In their studies, principal interest in applying calorimetry was in studying the interactions of chromium carbonyl catalyst on CaO support. Chromium carbonyl interactions (Le., reactions) with the CaO support reached as high as 60 kcal/mol. As might be expected, the adsorptions of CO on CuzO/ZnO and Cu ZnO methanol synthesis catalyst (10-26 kcal/mol) and on c!u-Zn-A1 oxidation catalyst (17 kcal mol) are also high. These have provided opportunities for t e study of these sorption systems using microcalorimetry to determine both the heterogeneity in adsorption sites and the thermokinetics of interactions (1143-1146). Hydrocarbon interactions with catalysts were also reported. Cerny and co-workers (1147) studied the heats of adsorption of methane, ethane, propane, ethylene, propylene, acetylene, methylacetylene,allene, and cyclopropaneon platinum films. Their purpose was to correlate differential heats of hydrocarbon adsorption with current hypotheses concerning the probable mechanisms of dehydrogenation. For the alkanes they observed a strong decrease in heat with increasing coverage. The kinetics of heat release was also slow. This was interpreted as indicating that only a limited number of surface sites, with high activation energy, probably involved in the mechanism. For acetylene and methylacetylene, differential heats were fairly constant with coverage, indicating that interactions were more uniform and occurred over a larger portion of the surface sites than in the case of alkanes or alkenes. The heats for monoalkenes were the lowest, and showed a mild decrease with increased coverage. Adsorption of dlene produced an essentially coverage-independent heat, which was higher than the heat of monoalkenes. The relative heats of adsorption of the various hydrocarbons, and their relative extent of surface coverage, were used to formulate a number of working hypotheses concerning the mechanism of dehydrogenation over platinum. Other studies where the energies for hydrocarbon/catalyst adsorption processes were studied calorimetrically include measurements of the interaction of cumene and benzene with aluminosilicate catalyst (1148) and the interactions of aliphatic hydrocarbons on Co Fisher-Tropsch catalysts (1149). Microcalorimetry was also used as a highly selective detector for quantifyingthe end point for chemisorption titrations. For example, Bossi and co-workers (1150)proposed using the heat release from the room temperature decomposition of N20over Cu as detection tool for the titration of surface area for Cu in Cu-ZnO catalyst. This reaction is very advantageous because the heat of interaction does not vary with coverage or with Cu loading. The measurement of evolved heat turned out to be much more precise than determination of surface area by volumetric techniques (i.e., the reaction O2 and N20 with Cu). In addition, the microcalorimetric method could be applied as a rapid, direct single-step procedure. This approach can probably be applied in many situations where NzO decomposition is catalyzed. In an analogous manner, Tournayan et al. (1151) followed the thermal behavior of O2 chemisorption in the Pt/Zr02 and Pt-Zr/Zr02 systems. Oxygen chemisorption was interpreted as quantifying the total alloy metal, Pt + Zr. In conjunction with these measurements, hydrogen chemisorption was used to specifically determine Pt surface area. The difference between the two measurements gave them a measure of the extent of Zr alloy formation

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resulting from different pretreatment temperatures.

OTHER TECHNIQUES This section includes analytical techniques which are either less frequently used for the characterization of catalysts, such as mass spectrometry or magnetic susceptibility, or are more used for material characterization than catalyst characterization per se, such as elemental analysis, or represent an emerging technique, such as molecular modeling. Mass Spectrometry, Mass spectrometry has been used in heterogeneous catalysis to determine the specific area of a solid, to measure the metallic surface of a catalyst, and to study the temperature desorption, catalytic reactions, and reactivity of adsorbed species (JI). Surface catalyzed chemical reactions can be studied by pulsed-laser field desorption mass spectrometry; the reaction intermediates in NH3 synthesis on metrl surfaces can be observed directly by this technique (J3, J4) Field desorption mass spectrometry has been used to exa ne the species involved in the reactions of oxygen with Ru irfaces a t 600 "C (J5) and CO and H2 on cobalt surfaces (JS, Ashton et al. (J2)utilized fast atom bombardment mass spectrometry (FABMS) to monitor the modification of the surface composition of zeolites. FABMS analysis of steamed zeolites revealed surface layers enriched in aluminum, and FABMS analysis of P modified HZSM-5 showed that the outer surfaces are rich in P, with the type and distribution of surface P species dependent upon the mode of incorporation of the P. Electrochemistry. Electrochemical techniques can be valuable in helping to elucidate specific properties of catalysts. For example, the cyclic voltammetry behavior exhibited by several Pt/Ti02 catalysts was cited as evidence supporting the existence of strong metal-support interaction (SMSI) for these materials (J7,J8). The surface species in unsupported hydrodesulfurization catalysts can be characterized by their zeta potentials and isoelectric points as determined by electrophoretic migration measurements (J9). The point of zero charge, surface acidity constants, and the concentration of the harged surface groups A10H2+and A10- were determined potentiometric acid-base titrations for a series of y-alu?as (JIO). The consequences of the above study have :vance to the use of y-aluminas for preparation of supported d y s t s by deposition of active ions via adsorption of positive r negative species. Magnetic Susceptibility. Magnetic susceptibility measurements are often used in conjunction with other techniques in order to characterize heterogeneous catalysts. Magnetic studies have been combined with Mossbauer spectroscopy to examine Fischer-Tropsch catalysts ( J I I ) and to determine the particle size of iron oxide particles supported on Grafoil (512). Magnetic susceptibility measurements and ESR were carried out on a set of five MoSz samples to test a hypothesis that all of the active sites on the MoS2 materials probed by O2 chemisorption might be magnetic, but that only a small fraction of these sites was detectable by ESR (J13). This was indeed found; still unresolved, however, is the microscopic origin of the large disparity. The adsorption of Hz, CO, CzH2, C2H4, and C,Hs on a Pd Si02 catalyst was studied by measuring the variation of t e paramagnetic susceptibility of the metal relative to the adsorbate and its coverage (J14). It is assumed that the adsorbed atoms cancelled out the magnetization of the surface Pd atoms in a discrete manner, thus allowing for conclusions as to the mode of binding. Elemental Analysis. The elemental compositions of various catalyst systems have been obtained by techniques employing high-energy excitation sources. The analysis of powdered catalysts by X-ray fluorescence (XRF) using the thin-film smear technique has been extended to 25 elements (JI5). This technique is useful due to it being a rapid, nondestructive, multielement analysis technique requiring only 20 mg of sample, and with results virtually independent of the matrix. A method for the determination of Ru in catalytic materials by photon-induced XRF employs a lo9Cd(7 mCi) annular source, thin-film technique, and an internal standard (JI6). A flame atomic absorption (AA) spectrometry method was developed to determine percent levels of Ti in Si02-A1203 base catalysts ( J l 7 ) ;interferences are eliminated by adding an excess amount of A1 and La to catalyst solutions and standards. An interference-free method for the determination of low concentrations of Mo in clay-supported catalysts by

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AA has been developed utilizing MIBK extraction of the Mo-SCN complex (J18). Flow injection analysis is gaining increasing popularity; examples of its use in elemental analpis include the detervanadium mination of trace (ng/mL) levels of copper (J19), (J20),and manganese (521, J22). Spectrophotometry has continued to be a popular tool for the analysis of catalysts. Various new reagents have been developed for the spectrophotometric determinations of K (J23),Co (J24),Ru (J25), Pd (J26-J31), and Os (J32). Molecular Modeling. The emerging technique of molecular modeling is beginning to have an impact on catalysis. Thomas and co-workers (J33) illustrated the use of computer graphics to model the chemistry of zeolites by examining the siting of cations, the accommodation and dynamics of guest reactant species, as well as the occurrence of various kinds of intergrowths. They also combined the use of neutron powder profile analysis and computer simulation to locate a guest organic base within gallozeolite-L (J34). Goddard (J35) described the use of qualitative quantum chemistry to gain insights into the mechanism of olefin metathesis and heterogeneous oxidations.

MULTIPLE TECHNIQUES This section is devoted to papers in which four or more analytical techniques were used by the author(s) to approach the particular problem of interest. Introductory reviews of catalysts characterization have been presented by Hofmann (K1) and Riekert ( K 2 ) ,while more comprehensive reviews are available by Burch ( K 3 ) with 354 references, Davis and Somorjai ( K 4 ) with 124 references, Bhatti and Dollimore (K5)with 58 references, Haller (K6)with 51 references, and Fierro and Garcia de la Banda ( K 7 )with 215 references. Specific reviews on the characterization of zeolites (K8,K9), hydrogenation catalysts (KIO),bimetallic catalysts ( K I I ) ,iron surfaces ( K I 2 ) ,zirconia (KI3),zirconium florine-promoted catalysts (K15), phosphate catalysts (K14), bismuth molybdate catalysts (KI6),polypropylene preparation catalysts (KI 7), electrocatalysts (KI8),supported transition metal ions (K19),and supported sulfide catalysts (K20)have been published. Hydrotreating catalysts represent a major portion of the industrial catalyst market; thus research in this area continues at a hectic pace. Topsoe and co-workers (K21) have further confirmed the Co-Mo-S model, i.e., promoter atoms are located a t the edges of the MoS,-like structures, by use of EXAFS, IR, XPS, HREM, and AEM, magnetic susceptibility, and other methods. Evidence for similar Ni-Mo-S, Co-W-S, Ni-W-S, and Fe-Mo-S structures was also found. Unsupported Ni/Mo sulfide catalysts have been prepared by an original coprecipitation technique performed at low temperature (K22);studies by various techniques (XRD, electron microscopy, 02-chemisorption, XPS, and ion-scattering spectroscopy) provide evidence for a Ni-Mo-S mixed phase over the whole range of composition. A conventional NiMo/A1203catalyst was impregnated with K2C03and characterized by Raman spectroscopy, diffuse reflectance and XPS, analytical electron microscopy, temperature-programmed desorption, and CO chemisorption (K23);apparently the octahedral coordination of Mo in the catalyst is transformed into a tetrahedral coordination, with concomitant decrease in hydrodesulfurization activity and increase in water-gas-shift reaction activity. Zeolitic catalysts are frequent targets of the multiple techniques characterization approach. A wide range of analytical techniques (XRD, DTA/TG, IR, texture, SEM/TEM, and 13C 27Al,29SiMASNMR) were used to characterize the intermehiates formed during crystallization of ZSMd catalysts (K24). Similar multiple techniques can be used to determine zeolite acidity; Vedrine et al. (K25) found that the acid sites for ZSM-5 are very strong and are stronger than those for ZSM-11, and no electron donor (basic) sites were identified for either zeolites. The zeolite framework for the bimetallic catalysts Cu-M/NaY (M = Pt, Ir, Rh, Ru) was found to favor the formation of small homogeneous Cu-M alloy clusters (K26). The n-hexane isomerization/ hydrogenolysis activity of these zeolitic catalysts differ considerably from the silicasupported alloys, and this is interpreted in terms of a geometric effect as well as a surface acidity effect. Multiple techniques are frequently used to characterize the


phase composition of catalysts and precursors in order to ultimately determine the catalytically active form($. This was carried out on the oxidation Catalysts V/Ti02 (K27), vanadium-phosphate ( K B ) ,and supported uranium oxides (K29);the HzOzdecompositioncatalysts chromia-coatedsilica and alumina (K30);the dehydrogenation catalysts V205/Mg0 (K31), and platinum supported on yttrium, lanthanum and erbium fluorides (K32);the hydrogenation and methanation catalysts Ni-Fe alloy particles impregnated on TiOz and A1203 (K33),graphite lamellar compounds of iron, nickel, and cobalt (K34),thermally decomposed iron carbonyl adsorbed on silica (K35),and controlled oxidation products of supported cobalt octacarbonyl (K36). An especially noteworthy use of multiple techniques was carried out on the methanol oxidation catalysts Moo3 and Fez(Md3&, by Du Pont workers (K37). They found that for Moo3, which has a layered structure, the Mo03(010) surface exhibited no chemisorption of methanol, but chemisorption was found on powder surfaces and ion bombarded MoOS(010) surfaces. These results led to the conclusion that methanol absorption leading to reaction is facile a t coordinatively unsaturated Mo ions, which all of the faces of the pseudocubic Fe2(Mo04)3can expose, hence accounting for the higher activity versus the layered Moo3.

ACKNOWLEDGMENT The authors are very grateful for the assistance of Denise Brown and Giulia L. Peterson in the preparation of this manuscript. LITERATURE CITED X-RAY ABSORPTION SPECTROSCOPY ( A l ) Chiu, N. S.; Bauer, S. H.; Johnson, Marvin, F. L. J. Catal. 1984, 89(2), 226-243. (A2) Clausen, B. S.; Topsoe, H.; Candia, R.; Lengeler, B Springer R o c . fhys. 1984, 2(EXAFS Near Edge Struct. 3), 181-186. (A3) Topsoe, Nan Yu; Topsoe, Henrik; Sorensen, Ole; Clausen, Bjerne S.; Candia, Roberto Bull. SOC.Chim. Be@. 1984, 93(8-9), 727-733. (A4) Chiu, N. S.; Bauer, S. H.; Johnson, M. F. L. J. Catel. 1988, 98(1), 32-50. (A5) Kochubei, D. I.;Kozlov, M. A.; Zamaraev, K. I.;Burmistrov, V. A.; Startsev, A. N.; Ermakov, Yu. 1. Appi. Cafal. 1985, 74(1-3), 1-14. (A6) Boudart, M.; Dalla Betta, R. A,; Foger, K.; Loffler, D. 0.; Samant, M. G. Science (Washington, D.C.) 1985, 228(4700), 717-719. (A7) Bommannavar, A. S.; Montano, P. A. Appt. Surf. Sci. 1984, 79(1-4), 250-266. (A8) Sand, M. L. Ph.D. Thesis, University of Delaware 1982. p 133. (A9) Bond, Geoffrey C.; Wells, Peter B. Appl. Catal. 1985, 78(2), 225-230. (A10) Lytle, F. W.; Greegor, R. 6.; Marques, E. C.; Sandstrom, D. R.; Via, G. H.; Sinfelt, J. H. J. Catal. 1985, 95(2), 546-557. ( A l l ) Koningsberger, D. C.; Sayers, D. E. Solid Sfate Ionics 1985, 76, 23-27. (A12) Mansour, A. N.; Cook, J. W., Jr.; Sayers, D. E.; Emrich, R. J.; Katzer, J. R. J. Catal. 1984, 89(2), 462-469. (A13) Onuferko, Julia H.; Short, Davld R.; Kelley, Michael J. Appl. S u b . Sci. 1984, 79(1-4). 227-249 (A14) Lytle, F. W frepr.-Am. Chem. Soc., Div. Pet. Chem. 1984, 29(3), 785-793. (A15) Dexpert, H.; Lagarde, P.; Bournonville, J. P. J. Mol. Cafal. 1984, 25, 347-355. (A16) Bommannavar, A. S.; Montano, P. A.; Yacaman, M. J. Surf. Sci. 1985, 756(1). 426-435. (A17) Via, G. H.; Meltzner. G.; Sinfelt, J. H.; Greegor, R. 6.; Lytle, F. W. Swinger f r o c . fhys. 1984, P(EXAFS Near Edge Struct. 3), 176-180. (Ale) Meker, G.; Via, G. H.; Lytle, F. W.; Slnfelt, J. H. J. Chem. fhys. 1985, 83(1), 353-360. (A 19) Ichlkawa, Masaru; Fukushima, Takakazu; Yokoyama, Toshihiko; Kosugi, Nobuhiro; Kuroda, Haruo J. fhys. Chem. 1988, 90(7), 1222-1224. (A20) Hamada, Hideaki; Samant, Mahesh, G.; Boudart, Michel Chem. Lett. 1988, (6). 885-888. (A21) Horsley, J. A,; Lytle, F. W. ACS Symp. Ser. 1988, No. 298, 10-20. (A22) Sankar, G.; Sen. P.; Vasudevan, S.; Rao, C. N. R. Roc.-Indian Acad. Sci., Chem. Sci. 1988, 96(1-2), 115-120. (A23) Usami, T.; Takayama, S.; Yokoyama, M.; Kosugi, N.; Kuroda, H. J . folvm. Sci., folym. Lett. Ed. 1985. 23(8),427-432. (A24)- Garbassi, F; Bart, J. C. J.; Tassinari, R.; Vlaic, 0.; Lagarde, P. J. Catal. 1988, 98(2), 317-325. (A25) Vlaic, G.; Bart, J. C. J.; Foa, M.; Francalancl, F.; Clement, R. J. Organomef. Chem. 1985. 28713). 369-375. (A26) Udagawa, Yasuo; Tohj, Kazuyukl; Ueno. Akifumi; Ida, Takashl; Tanabe. Shull S~rinaerR o c . Phvs. 1984, Z(EXAFS Near Edae Struct. 3), 206-208: ’ (A27) Van? Blik, H. F. J.; Koningsberger, D. C.; Prins, R. J. Cafal. 1986, 9711). 210-21s. (A28)‘ VGc, G ; Bart, J. C. J.; Cavigiolo, W.; Pianzola, 6.; Mobilio, S. J . Cafal. 1985. 96(2), 314-325. (A29) Clausen, Bjerne, S.; Lengeler, Bruno; Rasmussen, Birgitte. S. J. Phys . Chem. 1985, 89(11), 2319-2324.

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DIFFRACTION, SMALL-ANQLE X-RAY SCATTERING, AND MOSSBAUER SPECTROSCOPY (61) Fleisch. T. H.; Meyers, B. L.; Ray, 0. J.; Hall, J. 6.; Marshall, C. L. J. Catel. 1988, 99(1), 117-125. (82) Kubelkova. Ludmila; Seidl, Vlastimll; Novakova, Jana; Bednarova, Sona; Jlru. Pave1 J. Chem. SOC., Faraday Trans. 7 1984, 80(6), 1367-1376. (83) Wright, Paul A.; Thomas, John M.; RamUas, Subramaniam; Cheetham, Anthony K. J. Chem. SOC., Chem. Commun. 1984, (20), 1338-1339. (84) Gameson. Ian; Wright, Paul A.; Rayment, Trevor; Thomas, John M. Chem. fhys. Lett. 1988, 723(3), 145-149. (65) Dhere, A. G.; De Angelis, R. J. J. Catal. 1985, 92(1), 145-154. (86) Rodriguez-Reinoso, F.; Rodriguez-Ramos. I.; Moreno-Castilla, C.; Guerrero-Ruiz. A,; Lopez-Gonzalez. J. D. J. Cafai. 1986, 99(1), 171-183. (87) Martin, M. A.; Pajares, J. A.; Gonzalez Tejuca, L. J. Colloid Interface Sci. 1985, 707(2). 540-546. (68) Sudhakar, Chakka; Vannice, M. Albert Appl. Catal. 1985, M(1-3). 47-63. (89) Burwell, Robert L., Jr. Langmuk 1988, 2(1), 2-11. (610) Butt, John B. Appl. Catal. 1985. 75(1), 181-173. (611) Ziemeckl, S. 6.; Jones, G. A. J. Catal. 1985, 95(2), 621-622. (812) Zlelinskl, J.; Borodzinski, A. Appl. Catal. 1985, 73(2), 305-310. (813) Georgopoulos, Panayotis; Cohen, Jerome B. J. Catal. 1985, 92(2), 21 1-215(814) Wu, Q.; Gobolos, S.; Grange, P.; Delannay, F. Thermochim Acta 1984, 87, 281-296. (815) Muralidhar, G.; Concha, Bernard0 E.; Bartholomew, Greg L.; Bartholomew, Calvln H. J. Catal. 1984, 89(2), 274-284. (616) Makovsky, Leo E.; Stencel, John M.; Brown, Fred R.; Tlscher, Richard E.; Pollack, Sidney S. J. Catal. 1984, 89(2), 334-347. (817) Moroz, E. A.; Bogdanov, S. V.; Tsybulya, S. V.; Burmlstrov, V. A.; Startsev, A. N.; Ermakov, Yu. I.Appl. Catal. 1984, 77(2-3), 173-176. (618) McCarty, K. F.; Anderegg, J. W.; Schrader, G. L. J. Catal. 1985, 93(2), 375-387. (619) Cocco, Glorglo; Enzo, Stefano; Galvagno, Signorino; Poltarzewski, Zbigniew; Pietropaolo, Rosario J. Chem. Soc., Faraday Trans. 7 1985, 87(2), 321-333. (820) Brumberger. H.;DeLagllo. F.; Goodisman, J.; Phillips, M. G.; Schwar2, J. A.; Sen, P. J. Catal. 1985, 92(2), 199-210. (821) Ciccariello, Salvino; Benedettl, Ahrise J. ADD/. Crystallow. . - 1985, 78(4), 219-229. (822) Espinat, D.; Moraweck, 6.; Larue, J. F.; Renouprez, A. J. J. Appl. Crystallogr. 1984, 17(4), 269-272. (823) Brumberger, H.; Chang, Y. C.; Phillips, M. G.; DeLaglio, F.; Goodisman, J. J. Catal. 1988, 97(2), 561-564. (624) DeLaglio, F.; Goodisman, J.; Brumberger, H. J. Catal. 1988, 99(2), 383-390. (825) Montano, P. A. @perf/ne Interacf. 1988, 27(1-4), 147-159. (826) Topsoe, Henrik Clausen. Bjerne S.; Moerup, Steen wpertlne Inferact. 1988, 27(1-4), 231-248. (827) Stewart, 1.; Tricker, M. J.; Cairns, J. A. J. Catal. 1985, 94(2), 360-369. (828) Udovlc, Terrence J.; Dumeslc, J. A. J. Catal. 1984, 89(2), 303-313. (829) Yeh, E.; Jaggi, N. K.; Butt. J. 6.; Schwartz, L. H. J. Catal. 1985, 97(2). 231-240. (830) Valshnava. Prem P.; Ktorides, Petros I.; Montano, Pedro A.; Mbadcam, Ketcha J.; Melson, Gordon A. J. Cafal. 1985, 96(2), 301-313. (831) Tau, L. M.; Bennett, C. 0. J. Catat. 1984, 89(2), 285-302. (632) Cordischi, D.; Burriesci, N.; D’Alba, F.; Petrera, M.; Polizzotti, 0.; Schiavello, M. J. Solid State Chem. 1985, 56(2), 162-190. (833) Sulb, Steven L.; McMahon, Kerry C.; Tau, Li Mln; Bennett, Carroll 0. J . Cafal. 1984, 89(1), 20-34.

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CATALYST CHARACTERIZATION (834) Matyi, R. J.; Butt, J. B.; Schwartz, L. H. J. Catal. 1985, 91(2), 185-196. (B35) Nlemantsverdriet, J. W.; Van Kaam, J. A. C.; Flipse, C. F. J.; Van der Kraan, A. M. J. Catal. 1985, 96(1), 58-71. (836) Niemantsverdriet, J. W.; Van der Kraan, A. M.; Delgass, W. N. J. Catal. 1984, 89(1), 138-149. (837) Niemantsverdriet, J. W.; Aschenbeck, D. P.; Fortunato. F. A,; Delgass, W. W. J. Mol. Catal. 1984, 25, 285-293. (B38) Jiang, Xuan Zhen; Stevenson, Scott A.; Dumesic, J. A. J. Catal. 1985. 91(1), 11-24. (839) Christensen, Per Helvig; Moerup, Steen; Niemantsverdriet, Johannes W. J. Phys. Chem. 1985, 89(23), 4698-4900. (840) Frety, R.; Benaichouba. B.; Bussiere, P.; Cunha. D. Santos; Lam, Y. L. J. Mol. Catal. 1984, 25, 173-162.

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ELECTRON SPIN RESONANCE (DI) Che, Michel; Taarit, Younes Ben Adv. Collokj Interface Scl. 1985, 23, 235-255. (D2) Shvets. V. A. Usp. Khim. 1988, 55(3), 427-449; CA 104(22): 193937h. (D3) -Barth, Achim; Kirmse, Reinhard Stach, Joachim Z. Chem. 1984, 2415). ,. 195-196: CA 1011101: 7921811. (D4) Kucherov, A.' V.;Slinkin. A. A.;Kondrat'ev, D. A.; Bondarenko, T. N.; Rubinshtein, A. M.; Minachev, Kh. M. Zeolites 1985, 5(5), 320-324; Kucherov, A. V.; Slinkin, A. A.; Kondrat'ev, D. A,; Bondarenko, T. N.; Rubinshtein, A. M.; Minachev, Kh. M. Klnet. Katal. 1985, 26(2), 409-415; CA 702(26): 226597m. (D5) Narayana, M.; Kevan, Larry Langmulr 1985, 1(5),553-557. (D6) Michalik, Jacek; Narayana, M.; Kevan, Larry J. Phys. Chem. 1984, 88(22), 5236-5240. (D7) Kucherov, A V.; Slin'kin, A. A. Stud. Surf. Sci. Catal. 1984, 18, 77-84. (DE) Kalinlna, N. G.; Ryabov, Yu. V.; Korobitsyna, L. L.; Poluboyarov, V. A.; Erofeev, V. I.;Kurina, L. N.; Anufrienko, V. F. Kinet. Katal. 1988, 27(1), 240-243; CA 104(25): 224466k. (D9) Narayana, M.; Michalik, J.; Contarini, S.; Kevan, Larry J. Phys. Chem. 1985. 891181. -,. 3895-3899. (D10) Zina, M.; Olivier. D.; Ghorbel, A. Rev. Chim. Miner. 1985, 22(3), 321-330; CA 104(2): 11086~. (D11) Michalik, J.; Narayna, M.; Kevan, Larry J. Phys. Chem. 1985, 89(21), 4553-4560. (D12) Michallk, J.; Heming, M.; Kevan, Larry J. Phys. Chem. 1986, 90(10), 2132-2136. (D13) Michalik, J.; Lee, H.; Kevan, Larry J. Phys. Chem. 1985, 69(20), 4282-4285. (D14) Goldfarb, Daniella; Kevan, Larry J. Phys. Chem. 1986, 90(10), 2137-2144. (D15) Karge, H. G.; Zhang, Y.; Trevizan de Suarez, S.; Zloiek, M. Stud. Surf. Sci. Cafal. 1984, 18, 49-59. (D16) Karge. H. G.; Boldingh, E. P.; Lange, J. P.; Gutsze, A. Acta Phys. Chem. 1985, 31(1-2), 639-648. (D17) Bandiera, J.: Hamon. C.: Naccache. C. Proc. Int. Zeolite Conf.. 6th 1984, 337-344. (D18) Che, Michel; Giamello, Elio; Tench, Anthony J. Colloids Surf. 1985, 1312-3). 231-248. (D19) 'Blasco, T.;Conesa, J. C.; Salnz. M. T.; Soria, J. J. Mol. Struct. 1988, 143, 255-258. (D20) Volodln, A. M. React. Kinet. Catal. Lett. 1984, 25(3-4), 335-337. (D21) Kuli-Zade, A. M.; Shvets, V. A.; Kazanskii, V. B. Zh. Fiz. Khim. 1986, 60(3), 769-771; CA 104(18): 156563n. \

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CATALYST CHARACTERIZATION (022) Sass, A. S.; Shvets, V. A.; Savel'eva, G. A.; Popova, N. M.; Kazanskii, V. B., Klnet. Katal. 1985, 26(4), 924-931; CA 103(20): 186918y. (D23) Berlmhelli, Tlzlana; Gervasinl, Antonella; Morazzoni, Franca; Strumdo, Donatelia Martinengo, Secondo; Zanderlghl, Lucian0 J. Chem. Soc. 1984, 80(6), 1479-1489. (D24) Howard, J. A.; Sutcilffe, R.; Mile. B. J. Catal. 1984, 90(1), 158-159. (D25) Gesser, H. D.; Kruczynski, L. J. Phys. Chem. 1984, 88(13), 2751-2753. (D26) Xu, Xiaoding; Andreinl, A.; Mol, J. C. J. Mol. Catal. 1985, 28(1-3), 133-140. (D27) Shvets, V. A.; Tarasov, A. L.; Kazanskll. V. 6.; Knoezinger, H. Chem. Phys. Left. 1985, 115(6), 515-518. (D28) Corden, Barry 6.; Drago, Russell S.; Perito, Richard P. J. Am. Chem. SOC. 1985, 707(10), 2903-2907. (D29) Datta, Arunabha; Cavell, Ronald G.; Tower, Robert W.; George, Zacherla M. J. Phys. Chem. 1985, 89(3), 443-449. (D30) Che, M.; Canosa. 6.; GonzalezIllpe, A. R. J. Phys. Chem. 1988, 90(4), 618-621. 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(D69) Berlngheiii, T.; Gervaslni, A,; Morazzoni, F.; Pinna, F.; Strukul, 0. J. Catal. 1984, 88(2). 313-316. (D70) Flockhart, Brian D.; Salem, Mohamed A. J . Colloid Interface Sci. 1985. 103(11. 76-84. (D71) -1ndovha; VaGrio; Cordischi, Dante; Febbraro, Stefano; Occhluzzl. Manllo J. Chem. Soc., Faraday Trans. 11985, 8 1 , 37-48. (D72) Eick, J.; Engels, S.; Moerke, W. Z . Anorg. Allg. Chem. 1984, 572, 34-38; CA 101(16): 137796n. (D73) Surln, S. A.; Vaslienko. L. V.; Chukin, G. D.; Nefedov, 8. K. Kinet. Katal. 1985, 26(3), 753-757. SURFACE ANALYSIS

(El) Steinbrunn, A.; Lattaud, C. Surf. Sci. 1985, 155(1), 279-295. (E2) Castner, D. G.; Watson, P. R. ACS Symp. Ser. 1985, No. 288, 144-1 52. (E3) S i b , R. Prada; Delannay, F.; Grange, P.; Delmon, B. Polyhedron 1988, 5(1-2), 195-198. (E4) Carver, James C.; Davis, S. Mark; Goetsch, Duane A. ACS Symp. Ser. 1985, No. 288, 133-143. (E5) Brown, James, R.; Ternan, Marten Ind. Eng. Chem. Prod. Res. Dev. 1984, 23(4), 557-564. (E6) Brinen, J. S.; D'Avignon, D. A.; Meyers, E. A.; Deng, P. T.; Behnken. D. W. SIA. Surf. Interface Anal. 1984, 6(6), 295-301. (E7) Brinen, J. S.; Graham, S. W.; Hammond, J. S.; Paul, D. F. S I A , Surf. Interface Anal. 1984, 6(2), 68-74. (E8) Dwyer, D. J.; Cameron, S. D.; Gland, J. Surf. Sci. 1985, 159(2-3), 430-442. (E9) Greenlief, C. M.; White, J. M.; KO, C. S.; Gorte. R. J. J. Phys. Chem. 1985, 89(23), 5025-5028. (E10) Vannice, M. A.; Odler, P.; Bujor, M.; Fripiat, J. J. ACS Symp. Ser. 1985, No. 288 (Catal. Charact. Sci.), 98-110. ( E l l ) Sadeghi, Hassan R.; Henrlch, Victor E. Appl. Surf. Sci. 1984, 19(1-4), 330-340. (E12) Beck, D. D.; Bawagan, A. 0.; White, J. M. J. Phys. Chem. 1984, 88(13), 2771-2775. (E13) Raupp, G. 6.; Dumeslc, J. A. J. Phys. Chem. 1985, 89(24), 5240-5246. (E14) Cox, David F.; Hoflund, Gar 6.; Laltlnen, Herbert A. Langmuir 1985, 7(3), 269-273. (EM) Campbell, Charles T. J. Catal. 1985, 94(2), 436-444. (E16) Prince, K. C.; Kordesch, M. E. Appl. Surf. Sci. 1985, 22-23(1), 469-477. (E17) Campbell, Charles T.; Paffett, Mark T. Appl. Surf. Sci. 1984, 79(1-4), 28-42. _. .(E18) Richter, Lee J.; Ho, W. J. Vac. Sci. Techno/.,A 1985, 3(3, pt. 2), 1549-1553. (E19) Hall, R. 6.; DeSantolo, A. M.; Bares, S. J. Surf. Sci. 1985, 761(1), L533-L542. (E20) 15911). Gates, 233-255. S. M.; Russell. J. N., Jr.; Yates, J. T., Jr. Surf. Sci. 1985, (E21) Akhter, Sohail; White, J. M. Surf. Sci. 1988, 767(1), 101-126. (E22) Steinbach, F. Izv. Khim. 1984, 17(1), 85-94. (E23) Hrbek, Jan; De Paola, Robert; Hoffmann, Friedrich M. Surf. Sci. 1988, 166(2-3), 361-376. (E241 Kordulls, C.; Doumain, B.; Damon, J. P.; Masson, J.; Dalions, J. L.; Delannay, F. Bull. SOC.Chlm. Be/g. 1985, 94(6), 371-377. (E25) Niemantsverdriet, J. W.; Van Kaam, J. A. C.; Flipse, C. F. J.; Van der Kraan, A. M. J . Catal. 1985, 96(1), 58-71. (E26) Benecke. Wolfgang; Feiier, Heinz Gerhard; Ralek, Milos 2.Metallkd. 1984, 75(8), 625-629; CA 701(16): 137824~. (E27) Dang, Tuan A.; Petrakis, Leonidas; Klbby, Charles; Hercules, David M. J . Catal. 1984, 88(1), 26-38. (E28) Brown, A.; Vlckerman, J. C. Surf. Scl. 1984, 140(1), 261-274. (E29) Sexton, B. A.; Hughes, A. E.; Foger, K. J . Catal. 1984, 88(2), 466-477. (E30) Dubois, Lawrence H.; Nuzzo, Ralph G. Surf. Sci. 1985, 749(1), 133-1 45. (E31) Houalb, Marwan; Dang, Tuan A.; Klbby, Charles L.; Petrakis, Leonidas; Hercules, David M. Appl. Surf. Sci. 1984, 79(1-4), 414-429. (E32) Goodman, D. W.; Peden, C. H. F. J. Catal. 1985, 95(1), 321-324. (E33) Asscher, M.; Carrazza, J.; Khan, M. M.; Lewis, K. B.; Somorjai, G. A. J. &tal. 1988, 98(2), 277-287. (E34) Egawa, Chlkashi; Nishida. Tetsuya; Nalto, Shuichi; Tamuru, Kenzi, J . Chem. Soc., Faraday Trans. 11984, 80(6), 1595-1604. (E351 Tsai, M. C.; Seip, U.; Basslgnana, I.C.; Kueppers, J.; Ertl, G. Surf. Scl. 1985, 155(2-3). 387-399. (E36) Gland, John L.; Koilin, Edward B. Surf. Sci. 1985, 157(1), 260-270. (E37) Griffiths, K.; Jackman, T. E.; Norton, P. R.;Binder, P. E.; Seikirk, E. 6.; Davies, J. A. Nucl. Instrum. Methods Phys. Res., Sect. B 1984, 230(1-3), 303-306. (E38) Koel, B. E.; Bent, B. E.; Somorjai, G. A. Surf. Sci. 1984, 146(1), 21 1-228. (E39) Godbey, David; Zaera, Francisco; Yeates, Randall; Somorjai, 0. A,. Surf. Sci. 1988, 767(1), 150-186. (E40) Davis, S. M.; Zaera, F.; Gordon, B. E.; Somorjai, G. A. J. Catal. 1985, 92(2), 240-246. (E41) Stuve, E. M.; Madix, R. J.; Brundle, C. R. Surf. Sci. 1985, 752-153(1), 532-542. (E42) Barteau, M. A.; Feulner, P.; Stengi, R.; Broughton, J. Q.; Menzel, D. J. Catal. 1985, 94(1), 51-59. (E43) Kaminsky, Mark, P.; Winograd, Nicholas; Geoffrey, Gregory L.; Vannice, M. Albert J. Am. Chem. SOC. 1988, 108(6), 1315-1316. (E44) McBreen, P. H.; Erley, W.; Ibach, H. Surf. Scl. 1984, 748(2-3), 292-3 10. (E45) Moon, D. W.; Bernasek, S. L.; Dwyer, D. J.; Gland, J. L. J. Am. Chem. SOC. 1985, 107(14), 4363-4364. ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNE 15, 1987

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CATALYST CHARACTERIZATION (E46) Bozso, Ferenc; Arias, Jose; Hanrahan, Claran P.; Yates, John T., Jr.; Martin, Richard M.; Metlu. Horia Surf. Sci. 1984. 141(2-3). 591-603. (E47) Avery, Neil R. Surf. Sci. 1985. 163(2-3). 357-368. (E46) Connell, Glen; Dumesic, J. A. J . Catal. 1985, 92(1), 17-24. (E491 Landuyt, Jean Paul; De Gryse, R o p r ; Vennk, Joost Acta Chlm. Hung. 1985, 119(2-3), 193-202. (€50)Crowell, J. E.; Tysoe, W. T.; Somorjai, G. A. J . Phys. Chem. 1985, 89(9), 1596- 1601. (E51) Eberhardt, W.; Hoffmann, F. M.; DePaola, R.; Heskett, D.; Strathy, I.; Plummer, E. W.; Moser. H. R. Phys. Rev. Lett. 1985, 54(16), 1856-1859. (€52) Hardegree, E. L.; Ho, Pin; White, J. M. Surf. Sci. 1986, 165(2-3), 488-506. (E53) Soiymosi, Frigyes; Bugyi, Laszlo Appl. Surf. Sci. 1985, 21(1-4), 125-138. (E54) Di Castro, V.; Piredda, G. Chem. Phys. Lett. 1985. 114(1), 109-113. (E551 Bicker, R.; Deger, H.; Herzog, W.; Rieser, K.; Pulm. H.; Hohlneicher, G.; Freund, H. J. J . Catal. 1985, 94(1), 69-78. (E561 Takasu, Y.; Sakuma, T.; Matsuda, Y.; Toyoshima, I.Surf. Sci. 1985, 152-153( l), 479-486. MICROSCOPY (FI) Lynch, J. Rev. Inst. F r . Pet. 1985, 40(1), 63-76; CA 102(16): 138398s. (F2) Sanders, J. V. J . Electron Microsc. Tech. 1988, 3(1), 67-98. (F3) Dhere, A. G.; Reucroft, P. J.; De Angelis, R. J.; Bentley. James, Anal. Electron Mlcrosc. Proc. Workshop 1984, 196-200. (F4) Targos, William, ACS Symp. Ser. 1985, No. 288, 374-384. (F5) Herz, Richard K.; Shinouskis, Edward J.; Datye, Abhaya; Schwank, Johannes Ind. Eng. Chem. Prod. Res. Dev. 1985, 24(1), 6-10. (F6) Felthouse, Timothy R.; Murphy, Judith A. J . Catal. 1988, 98(2), 411-433. (F7) Harris, P. J. F. Inst. Phys. Conf. Ser. 1988, 78, 469-492. (F8) Gillet, M. F.; Channakhone, S. J . Catal. 1988, 97(2), 427-436. (F9) Gillet, E.; Channakhone, S.; Matoiin. V.; Gillet, M. Surf. Sci. 1985, f52-153( I), 603-614. (FIO) Durrer, W. G.; Poppa, H.; Dicklnson, J. T.; Park, C. J . Vac. Sci. Techno/. 1985. 1545 - 1548. ~~. ( F l 1 ) - Baker, R. T. K.; Prestidge, E. B.; McVlcker, G. B. J . Catal. 1984. 89121. 422-432. (F12) J. C.; Van't Bllk, H. F. J.; Hulzinga, T.; Van Grondelle. J.; Prins, R . J . Catal. 1985, 95(2), 333-345. (F13) Datye, A. K.; Allard, L. F.; Schwank, Johannes Anal. Electron Microsc. Proc. Workshop 1984, 205-2013, (F14) Berry, Frank J.; Smith, David J. J . Catal. 1984, 88(1). 107-118. (F15) Bonnevlot, L.; Che, M.; Ollvler, D.; Martin, G. A,; Freund, E. J . Phys. Chem. 1988, 90(10), 2112-2117. (F16) I i j i i , S.J . Electron Microsc. 1985, 34(4), 249-265. (F17) Iijima, S.; Ichikawa, M. J . Catal. 1985, 94(1), 313-316. (FIE) Smith, D. J.; Marks, L. D. Ultramicroscopy 1985, 16, 101-114. (F19) Marks, L. D. Ultramicroscopy 1985, 18, 445-452. (F20) Hutchison, J. L.; Briscoe, N. A. Uhramicroscopy 1985, 18, 435-438. (F21) Drechsler, M. Surf. Sci. 1985, 162(1-3), 755-763. (F22) Qiao, G. W.; Zhou, J.; Kuo, K. H. Z . Naturforsch. 1986. 41A(3), 478-482, 67-71. (F23) Terasaki, 0.; Thomas, J. M.; Millward, G. R. Proc. R . SOC. London 1984, 395(1808), 153-164. (F24) Gai, P. L. J . Catal. 1984, 89(2), 545-549. (F25) Andersson, Arne; Bovln, Jan Olov; Walter, Paul J . Catal. 1986, 98(1), 204-220. (F26) Soerensen, Ole; Calusen, Bjerne S.; Candia, Roberto; Topsoe, Henrik Appl. Catal. 1985, 13(2), 363-372. (F27) Topsoe, Nan Yu; Topsoe, Henrik; Soerensen, Ole; Ciausen, Bjerne S.; Candla Roberto Bull. SOC. Chim. Be/g. 1984, 93(8-9), 727-733. (F28) Kilaas, R.; Gronsky, R. Ultramicroscopy 1985, 16, 193-202. (F29) Gai, P. L.; Goringe, M. J.; Barry, J. C.; Waddington, W. G.; Boyes, E. D. Inst. Phys . Conf. Ser. 1988, 465-488, 67-74. (F30) Fuentes, S.; Vazquez, A.; Perez, J. G.; Yacaman, M. J. J . Catal. 1988, 99(2). 492-497. (F31) Cowley, J. M. Prepr.-Am. Chem. SOC.,Div. Pet. Chem. 1984, 29(3), 817-820. (F32) Cowley, J. M. J . Electron Mlcrosc. Tech. 1988, 3, 25-44. (F33) Gallezot, Pierre; Laclercq, Christiine; Mutin, Ildiio; Nicot. Christian; Richard, Dominique J . Microsc. Spectrosc. Electron 1988, 10(5), 479-484. (F34) Yacaman, Miguel, J. Sprlnger Ser. Chem. Phys. 1984, 35, 183-204. (F35) Kasano, Hlronobu; Kurata, Hirokl; Kobayashi, Takashl; Uyeda, Natsu, Bull. Inst. Chem. Res. 1985, 63(3), 216-226. (F36) Tatlock, G. J.; Baxter, A. G.; Devenish, R. W.; Punni, J. S. I n s t . Phys . Conf. Ser. 1988, 78, 455-458. (F37) Gal. P. L.; Labun. P. A. J . Catal. 1985, 94(1), 79-96. (F38) Boudart, M.; Holstein, W. L.; Moorhead. R. D.; Poppa, H. Appl. Catal. 1984, 11(1), 117-122. (F39) Chan, Ignatius, Y. J . Electron Mlcrosc. Tech. 1985, 2(6), 525-532. (F40) Cowley, J. M.; Peng, L. Uhramicroscopy 1985, 16, 59-68. (F41) Shimlzu, N.; Tanlshlro, Y.; Kobayashl, K.; Takayanagl, K.; Yagi, K. ultramicroscopy 1985, 18, 453-462. (F42) Tanji. T.; Cowiey, J. M. UMamlcroscopy 1985, 17, 287-302. (F43) Shannon, M. D.; Eades, J. A.: Melchel, M. E. Ultramicroscopy 1985, 16, 175-192. (F44) Petroff, P. M.; Chen, C. H.; Werder, D. J. Ultramicroscopy 1985, 1 7 , 185-192. ~

~

'6

THERMAL ANALYSIS

(Gl) Eyraud. C. Thermochim. Acta 1988, 100(1),223-253. (G2) Choi, Jeong GI; Rhee, Hyun Ku; Moon, Sang Heup Korean J . Chem. Eng. 1984, 1(2), 159-164.

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(G3) Kester, Keith B.; Zagll, Ercument; Falconer, John L. A.m . / . Catal. 1988, 22(2), 31 1-319. (G4) De Korte, Paulus H. M.; Doesburg, Egilius B. M.; De Winter, Cornelus P. J.; Van Reljen, Louis L. SolM State Ionics 1985, 16, 73-80. (G5) Vannlce, M. A.; Hasselbrlng, L. C.; Sen, B. J . Phys. Chem. 1985, 84(14), 2972-2973. (G6) Dall'Agnol. Carla; Gervaslni, Antonella; Morazzoni, Franca; Pinna, Francesco; Strukul, Giorio; Zanderighi. Luclano J . Catal. 1985, 96(1). 106-1 14. (G7) Chang, T. C.; Chen, J. J.; Yeh, C. T. J . Catal. 1985, %(I), 51-57. (G8) Kunimori, Kimio; Maezawa, Ikufumi; Uchijima, Toshio J . Chem, SOC., Chem. Commun. 1985, (9), 568. (G9) Oliver, James A.; Kembail, Charles; Brown, Ronald; Jamleson, Edward W. J . Chem. SOC. 1985, 81(8), 1871-1881. (G10) Ross, Jullan R. H. Anal. Proc. 1985, 22(8),239-240. (G11) Ledford, J. S.; Houalla, Marwan; Hercules, D. M.; Petrakis, L., Prepr.-Am. Chem. Soc., Dlv. Pet. Chem. 1986, 31(1), 329-334. (G12) Caceres, C. V.; Fierro, J. L. G.; Lopez Agudo, A.; Blanco, M. N.; Thomas, H. J. J . Catal. 1985, 95(2), 501-511. (G13) Menon, P. G.; Froment, G. F. J . Mol. Catal. 1984, 25, 59-66. (G14) Van't Blik, H. F. J.; Koningsberger, D. C.; Prins, R. J . Catal. 1986, 97(1), 210-218. (G15) Matusek, K.; Bogyay, I.;Guczi, E.; Diaz, G.; Garin. F.; Maire, G. C , Mol. Chem. 1985, 1(4), 335-348. (G16) Van't Blik, H. F. J.; Niemantsverdriet, J. W. Appl. Catal. 1984, 10(2), 155-162. (G17) Frety, R.; Benaichouba, 8.; Bussiere, P.; Cunha, D. Santos; Lam, Y. L. J . Mol. Catal. 1984, 25, 173-182. (G18) Liesk, H.; Voelter, J. J . Catal. 1984, 90(1), 96-105. (G19) Van't Biik, H. F. J.; Prins, R. J . Catal. 1986, 97(1), 188-199. (G20) Vis, J. C.; Van't Bllk, H. F. J.; Huizinga, T.; Van Grondelle, J.; Prins, R., J . Catal. 1985. 95(2). 333-345. (G21) Fierro, J. G: G.; Tascon, J. M. D.; Tejuca, L. Gonzalez J . Catal. 1985, 93(1). . ,. 83-91. (G22) Iwamoto, M.; Takenaka, T.; Matsukami, K.; Hlrata, J.; Kagawa, S.; Izumi. J. Appl. Catal. 1985, 16(2), 153-156. (G23) Tang, Ren Yuan; Wu, Rong An; Lin, Li Wu J . Catai. 1985, 94(2) 558-562. (G24) Wu, Q.; Goboios, S.;Grange, P.; Delannay, F. Thermochim. Acta 1984, 8 1 , 281-296. (G25) Arnoldy, P.; De Jonge, J. C. M.; Moulijn, J. A. J . Phys. Chem. 1985, 89(21), 4517-4526. (G26) Bond, Geoffrey C.; Xu, Yide J . Mol. Cafal. 1984, 25, 141-150. (G27) Raupp, G. B.; Dumesic, J. A. J . Phys. Chem. 1985, 89(24), 5240-5246. (G28) Kaithod, Dlllp G.; Weller, Sol W. J . Catal. 1985, 95(2), 455-464. (G29) Vis, J. C.; Van't Blik, H. F. J.; Huizinga, T.; Van Grondelle, J.; Prins, R. J . Mol. Cafal. 1984, 25, 367-378. (G30) Potoczna-Petru, Danuta Pol. J . Chem. 1985, 59(7-9), 885-892. (G31) Martens. J. H. A.; Van't Bllk, H. F. J.; Prins, R . J . Catal. 1988, 97(1), 200-209. (G32) Choi, J. G.; Rhee, H. K.; Moon, S. H. Appi. Catal. 1985, 13(2). 269-280. (G33) Ziemecki, S. B.; Jones, G. A. J . Catal. 1985, 95(2), 621-622. (G34) Barbier, J.; Churin, E.; Parera, J. M.; Riviere, J. Reacf. Kinet. Cafal. Lett. 1985, 29(2), 323-330. (G35) Rudnitskil, L. A.; Solboleva, T. N.; Alekseev, A. M. React. Kinet. Catal. Lett. 1984, 26(1-2), 149-151. (G36) Rieck, Jeffery, S.; Bell. Alexis T., J . Catal. 1986, 99(2), 276-292. (G37) Rieck, Jeffery S.;Bell, Alexis T. J . Catal. 1985, 96(1), 88-105. (G38) Rieck, Jeffery S.; Bell, Alexis T. J . Catal. 1988, 99(2), 262-277. (G39) McClory, Mary McLaughlin; Gonzalez, Richard D. Actas Simp. Iberoam. Catal. 1984, 1 , 520-529. (G40) Yao, H. C. Appl. Surf. Sci. 1984, 19(1-4), 398-406. (G41) Yao, H. C.; Adams, K. M.; Gandhi, H. S.Front. Chem. React. Eng. 1984, 2, 129-141. (G42) Lee, Bu Yong; Inoue, Yasunbu; Yasumorl, Iwao Bull. Korean Chem. SOC. 1983, 4(6), 277-263. (G43) Lee Bu Yong; Inoue, Yasunobu; Yasumori, Iwao Bull. Chem. SOC. Jpn. 1984, 57(5),1283-1289. (G44) Gopalakrishnan, R.; Viswanathan, B., Adv. Cafal., Proc .-,Vat/. Symp. Catal. 1985, 733-739. (G45) Tri, T. M.; Massardier, J.; Gallezot, P.; Imelik, B., J . Mol. Catal. 1984, 25, 151-160. (G46) Splnlcci, R.; Tofanarl. A. React. Kinet. Catal. Left. 1985, 27(1), 65-69. (G47) Hall, Peter G.; Heaton, Philip; Rosseinsky, David R., J . Chem. SOC. 1985, 81(1), 97-103. (G48) Roberts, D. L.; Griffin, G. L., Appl. Surf. Sci. 1984, 19(1-4), 296-306. (G49) Glllet, E.; Channakhone, S.;Matoiin, V. J . Catal. 1986, 97(2), 437-447. (G50) Ramanathan, Kumar; Weller, S. W. J . Catal. 1985, %(I), 249-259. (G51) Okamoto, Yasuaki; Ohhara, Mlnoru; Maezawa, Akinori; Imanaka, Toshinobu; Teranish, Shlichiro J . Phys. Chem. 1988, 90(1 I), 2396-2407. (G52) Guil, J. M.; Herrero. J. E.; Ruiz Panieao. A. J . Colloid Interface Sci. 1984. 102(1), 111-120. (G53) Stradella, L. J . Therm. Anal. 1984, 29(2), 301-308. (G54) Gura, R. P.; Vlasenko, V. M.;Kuznetsov, V. A.; Raksha, V. V., Teor. Eksp. Khim. 1985, 21(3), 338-343; CA 103(6): 59978~. (G55) Ogata. Yoichi; Aika. Kenichi; Onishi, Takaharu Surf. Sci. 1984, 140(2). L265-L289. (G56) Gopalakrlshnan. R.; Viswanathan, B. J . Colloid Interface Sci. 1984. 102(2). 370-372.

CATALYST CHARACTERIZATION (G57) Sobalik, Zdenek; Pour, Viadlmlr; Sokolova, Ludmlla A.; Nevskaya, Olga V.; Popova, Nina M. Collect. Czech. Chem. Commun. 1985, 50(6), 1259-1 267. (G58) Hendrlckx, H. A. C. M.; Jongenelis, A. P. J. M.; Nieuwenhuys, B. E. Surf. Sci. 1985, 154(2-3), 503-523. (G59) Schubart, Wolfgang; Knoezinger, Helmut Z . Phys . Chem. Univ. Muenchen 1985, 144, 117-130. (G6O) Taklta, Yusaku; Tashiro, Tetsuro; Saito, Yumie; Hori, Fumiaki J . Catai. 1986, 97(1), 25-35. (G61) Andersson, Soeren; Pompe, Robert; Vannerberg, Nils Goesta Appl. Catal. 1985, 16(1), 49-58. (G62) Fan, Shurong; Wang, Qiubo; Yu, Zuolong; Li, Shufang; Xie, Xiaofan, Cuihua Xuebao 1985, 6(1), 83-86; CA 102(26): 2265652. (G63) Otremba, M. Geterog. Katal. 1983. 5th,Pt. 1, 387-392. (G64) Grady, M. C.; Gorte, Raymond J. J . Phys. Chem. 1985, 89(7), 1305-1308. (G65) Gabelica, Z.; Nagy J., B.; Berouane, E. G.; Giison, J. P. Clay Miner. 1984, 19(5), 803-824. (G66) Kubelkova, L.; Novakova, J.; Tupa, M.; Tvaruzkova, Z. Acta Phys. Chem. 1985, 31(1-2), 649-657. (G67) Von Ballmoos, R.; Kerr, G. T. Stud. Surf. Sci. Catai. 1985, 307-318. (G68) Hakvoort, G.; Van der Klugt, W.; Timmerman, Y.; Van Reijen, L. L. Thermochim. Acta 1985, 8 5 , 319-322. (G69) Tsuchiya, Susumu; Yoshioka, Norihiko J . Catai. 1984, 87(1), 144-151. (G70) Tokitaka, Shinji; Imamura, Hayao; Tsuchlya, Susumu Bull. Chem. SOC.Jpn. 1985, 58(1), 82-87. (G71) He, Ming Yuan; Ekerdt, John G. J . Catal. 1984, 87(1), 238-254. (G72) He, M. Y.; Ekerdt, J. G. Prepr.-Am. Chem. SOC.Div. Pet. Chem. 1984, 29(2). 532-540. (G73) Monnier, J. R.; Apai, G.; Hanrahan, M. J. J . Catal. 1984, 88(2), 523-525. (G74) Tagawa, T.; Pleizier, G.; Amenomlya, Y. Appl. Catal. 1985, 78(2), 285-293. (G75) Farneth, W. E.; Staley. R. H.; Sleight, A. W. J. Am. Chem. SOC. 1988, 108(9), 2327-2332. (G76) Iglesia, E.; Boudart, M. J . Catal. 1984, 88(2), 325-332. (G77) Splnicci, R.; Tofanari, A. Mater. Chem. Phys. 1985, 12(4), 321-329. (G78) Beck, D. D.; White, J. M.; Ratcliffe, C. T. J . Phys. Chem. 1988, 90(14), 3137-3140. (G79) Konovalova, N. D.; Belokopytov, Yu. V.; Kholyavenko, K. M. React. Kinet. Catal. Lett. 1985, 27(1), 7-10. (G80) Szalkowicz, Malgorzata; Kubas, Zdzislaw Thermochim. Acta 1985, 92, 391-394. (G81) Dollimore, D.; Gamlen, G. A.; Taylor, T. J., Thermochim. Acta 1984, 75(1-2), 59-69. (G82) Agrawal, G. L.; Banerjee, S . P. J . Inst. Chem. (India) 1985, 57(2), 65-67. (G83) Van Wagner, J.; Chapman, J. A.; Bell, J. A. E. Stud. Surf. Sci. Catal. 1984, 497-503. (G84) Zhou, Liangda; Zhang, Tianqiao, Shlyou Huangong. 1985, 74(12), 744-749; CA 104(20): 171040h. (G85) Le Van Mao, Raymond; Levesque, Pierre; Sjlariel, Bernard; Bird, Peter Hans Can. J . Chem. 1985, 63(12), 3464-3470. (G86) Inui, T.; Matsuda, H.; Takegami, Y. Proc. Int. Zeolite Conf. 1984, 316-324. (G87) Lercher, Johannes A.; Rumplmayr, Gerd; Noller, H. Acta Phys. Chem. 1985, 37(1-2), 71-80. (G88) Novakova, Jana; Kubelkwa, Ludmiia; Habersberger, Karel; Dolejsek, Zdenek J . Chem. SOC.,Faraday Trans. 11984, 80(6),1457-1465. (G89) Nitadori, Taihei; Kurihara. Shiegeo; Misono, Makoto J . Catal. 1986, 98(1), 221-228. (G90) Duprez, D.; Barbier, J.; Hamida, Z. Ferhat; Bettahar, M. Appi. Catal. 1984, 12(2). 219-225. (G91) Ikushima, Yutaka; Arai, Masahiko; Nishiyama, Yoshiyuki Appi. Catai. 1984, 71(2-3), 305-316. (G92) Burch, R.; Collins, A. Appi. Catal. 1985, 18(2), 373-387. (G93) Hoodless, R . C.; Moyes, R . B.; Wells, P. B. Bull. SOC. Chim. Belg. 1984. 93(8-9), 673-679.

OPTICAL SPECTROSCOPY (HI) Weinberg, W. Henry Methods Exp. Phys. 1985, 22, 23-125. (H2) Kung, Mayfair C.; King, Harold H. Catal. Rev.-Scl. Eng. 1985, 27(3), 425-460. (H3) Baker, Mark D.; Ozin, Geoffrey A.; Godber, John Catal. Rev-Sci. Eng. 1985, 27(4). 591-651. (H4) Nguyen, T. T. J . Singapore Nati. Acad. Sci. 1983, 10-12, 84-87. (H5) Bell. A. T. Swinger Ser. Chem. Phys. 1984, 35(Chem. Phys. Solld Surf. 5), 23-38.. (H6) Blackmond, D. G.; KO, E. I.J . Catai. 1985, 96(1), 210-221. (H7) Greenier, Robert G.; Burch, Kathryn D.; Kretzschmar, K.; Klauser, R.; Bradshaw, A. M.; Hayden, B. E. Surf. Sci. 1985, 152-153(1), 338-345. (H8) Yates, John T.; Jr.; Gelin, Patrick; Beebe, Thomas ACS Symp. Ser. 1985. No. 288. 404-421. (H9) &lin. Patrick: Sledle, Allen R.; Yates, John T., Jr. J . Phys. Chem. 1984, 88(14), 2978-2985. (Hlo) Guglieliminotti, E.; Spoto, G.; Zecchlna. A. Surf. Sci. 1985, 161(1), 202-220 -. - - -. .

(H11) Tsyganenko, A. A.; Denisenko, L. A.; Zverev, S. M.; Flllmonov, V. N. J . Catal. 1985, 94(1), 10-15. (H12) Primet, Mlchel; De Menorval, Louis Charles; Fraissard, Jacques: Ito, Taro J . Chem. SOC. 1985, 81(11), 2867-2874. (H13) Ichlkawa. M.; Lang, A. J.; Shriver, D. F.; Sachtler, W. M. H. J . Am. Chem. Soc. 1985, 1#7(24), 7216-7218. (H14) Ghiotti, Giovanna; Boccuzzi, Flora; Scala, Roberto J . Catai. 1985, 92(1), 79-97.

(H15) Boccuzzi, F.; Ghiotti, G.; Chiorino, A. Surf. Sci. 1985, 756(2), 933-942. (H16) Ghiotti, G.; Boccuzzi, F.; Chlorlno, A. J . Chem. SOC., Chem. Commun. 1985, (15), 1012-1014. (H17) Gutschick, D.; Mlessner, H. React. Klnet. Catal. Lett. 1984, 26(3-4), 387-390. (HIE) Solymosi, Frlgyes; Pasztor, Monika, J . Phys. Chem. 1985, 89(22), 4789-4793. (H19) Lefebvre, F.; Auroux, A.; Ben Taarit, Y. Stud. Surf. Sci. Catal. 1985, 24, 411-418. (H20) Gutschick, D.: Miessner, H.; Weber, M. J . Catal. 1985, 94(1), 297-299. (H21) Dai, C. H.; Worley, S. D. Chem. Phys. Led. 1985, 714(3), 286-290. (H22) Zaki, M. I.; Vielhaber, B.: Knoezinger, H. J . Phys. Chem. 1986, 90( 14), 3176-3183. (H23) Guglleiimonotti, Eugenio, Giamello, Elio J . Chem. SOC. 1985, 81(10), 2307-2322. (H24) Edwards, James F.; Schrader, G. L., J . Catal. 1985, 94(1), 175-186. (H25) Solymosl, Frigyes; Lancz, Margit J . Chem. SOC. 1988, 62(3), 883-897. (H28) Fukushima, Takakazu; Arakawa, Hironori; Ichikawa, Masaru J . Chem. Soc., Chem. Commun. 1985, ( I I ) , 792-731. (H27) Fukushima, Takakazu; Arakawa, Hironori; Ichikawa, Masaru J . Phys . Chem. 1985, 89(21), 4440-4443. (H28) Deiiglanni, H.; Mieville, R. L.; Peri, J. B. J . Catal. 1985, 95(2), 465-472. (H29) Lamb, H. Henry; Gates, Bruce C. J . Am. Chem. SOC. 1986, 708(l), 81-89. (H30) He, Ming Yuan; Ekerdt, John G. J . Catal. 1984, 87(2). 381-388. (H31) Okuhara, Toshio; Kimura, Tomoo; Kobayashi, Kenji; Misono, Makoto; Yoneda, Yukio Bull. Chem. SOC.Jpn. 1984, 57(4). 938-943. (H32) Arakawa, Hironori; Fukushima, Takakazu; Ichikawa, Masaru; Takeuchi, Kazuhiko; Matsuzaki, Takehlko; Sugi. Yoshihiro Chem. Lett. 1985, (I), 23-26. (H33) Fukushlma, Takakazu; Fujimoto, Kaoru; Tominaga, Hiroo Appl. Catal. 1985, 74(1-3), 95-99. (H34) Sato, Kimihiko; Inoue, Yasunobu; Kojima, Isao; Miyazaki, Elzo; Yasumorl, Iwao J . Chem. SOC. 1984, 80(4), 841-850. (H35) Kljenski, Jacek; Glinski, Marek; Peplonski, Ryszard J . Mol. Catai. 1984, 25, 227-239. (H36) Cant, Noel W.; Angove, Dennys E. J . Catai. 1986, 97(1), 36-42. (H37) McClory, Mary McLaughlln: Gonzalez, Richard D. J . Phys. Chem. 1986, 90(4), 628-633. (H38) Saymeh, Ryadh A.; Gonzalez, Richard D. J . Phys. Chem. 1986, 90(4), 622-628. (H39) Groff, R. P.; Manogue, W. H. J . Catai. 1984, 87(2), 461-467. (H40) Topsoe, Nan Yu; Topsoe, Henrik J . Electron Spectrosc. Relat. Phenom. 1986, 39, 11-13. (H41) Fierro, Jose Luis G.; Lopez Agudo, Antonio; Gonzalez Tejuca, Luis; Rochester, Colin H. J . Chem. SOC. 1985, 87(5), 1203-1213. (H42) Peri, J. B., ACS Symp. Ser. 1985, No. 288, 422-434. (H43) Hecker, William C.; Bell, Alexis T. J . Catal. 1985, 92(2), 247-259. (H44) Wielers, A. F. H.; Van der Grift, C. J. G.; Geus, J. W. Appl. Surf. Sci. 1986, 25(3), 249-264. (H45) Liang, Jim; Wang, H. P.; Spicer, L. D., J . Phys. Chem. 1985, 89(26), SAPO-SAPS - - .- - - .-. (H46) Sobalik, Zdenek; Pour, Vladimir; Sokolova. Ludmila A,; Nevskaya, Olga V.; Popova, Nina M. Collect. Czech. Chem. Commun. 1985, 50(6), 1259-1267. (H47) Rethwisch, D. G.; Dumesic, J. A. J . Phys. Chem. 1986, 90(8), 1625-1630. (H48) Okamoto, Yasuaki; Ohhara, Minoru; Maezawa, Akinori; Imanaka, Toshinobu; Teranishl, Shilchiro J . Phys . Chem . 1986, 90( 1I), 2396-2407. (HG) Nakajima, Takashi; Miyata, Hisashi; Kubokawa, Yutaka J. Chem. SOC. 1985. 811101. 2409-2419. (H50) Baltanas, Miguel A.; Stiles, Alvin B.; Katzer, James R . J . Catal. 1984, 88(2), 362-373. (H51) Haller, Gary L.; McMillan, Martin; Resasco, Daniel E.; Sakellson, Stanley Actas Simp. Iberoam Catal. 9th 1984, 2, 1475-1476. (H52) Sadeghi, Hassan R.; Henrich, Victor E. Appl. Surf. Sci. 1984, 19(1-4), 330-340. (H53) Hicks, Robert F.; Yen, Qi Jie; Bell, Alexis T.; Fleisch, The0 H. Appl. Surf. Sci. 1984, 79(1-4), 315-329. (H54) Lee, Bu Yong; Inoue, Yasunobu; Yasumori, Iwao Bull. Chem. SOC. Jpn. 1984, 57(5), 1283-1289. (H55) Asakura, Klyotaka; Yamada, Makoto, Iwasawa, Yasuhiro; Kuroda, Haruo Chem. Lett. 1985, (4), 511-514. (H56) Beebe, Thomas P., Jr.; Yates, John T., Jr. J . Am. Chem. SOC. 1988, 108(4), 663-671. (H57) Beebe. T. P.; Albert, M. R.; Yates, J. T., Jr. J . Catal. 1985, 96(1), 1-11. (H58) Howe, R. F. Chem. N . Z . 1986, 50(1),10-11. (H59) Dzwlgaj, S.;Haber, J.; Romotowski, T. Zeolites 1984, 4(2), 147-156. (H60) Grady, M. C.; Gorte, Raymond J. J . Phys. Chem. 1985. 89(7). 1305-1308. (H61) Henderson, M. A.; Worley, S . D. J . Phys. Chem. 1985, 89(3). 392-394. (H82) Henderson, M. A.; Worley, S. D. Report, TR-2; Order No. ADA149813/8/GAR, Avail. NTIS From: Gov. Rep. Announce. Index ( U . S . ) 1985, 85(9), 53. (H63) Hayes, Kenneth E. Can. J . Spectrosc. 1984, 29(6), 153-156. (H64) Bazilio, C. A.; Thomas, W. J.; Ullah, U.; Hayes, K. E. Proc. R SOC. London, A 1985, 399(1816), 181-194. (H65) Busca, Guido; Zerlia, Tiziana; Lorenzelli, Vlncenzo, Girelli. Alberto J . Catal. 1984, 88(l),131-136. ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNE 15, 1987

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CATALYST CHARACTERIZATION (H68) Busca, Guldo; Zerlia, Tiziana; Lorenzelli, Vincenzo; Girelll, Albert0 J. Cafal. 1984, 88(1), 125-130. (H67) Datta, Arunabha; Cavell, RonaM G.; Tower, Robert W.; George, Zacherla M. J . Phys. Chem. 1985, 89(3), 443-449. (H68) Datta, Arunabha; Cavell, Ronald G. J. Phys. Chem. 1985, 89(3), 450-454. (H69) Karge, H. 0.;Zhang, Y.; Trevizan de Suarez, S.;Zioiek, M. Stud. Surf. Sci. Cafal. 1984, 18, 49-59. (H70) Yamaguchl, Tsutomu; Jin, Tuo: Tanabe, Kozo J. Phys. Chem. 1988, 90(14), 31148-3152. (H71) NakaJlma, Takashi; Miyata, Hisashi; Kubokawa, Yutaka Chem. Lett. 1985, (I), 95-98. (H72) Boecker, D.; Wicke, E. Ber. Bunsen-Ges. fhys. Chern. 1985, 89(6). 629-633. (H73) Boecker, D.; Wicke, E. Springer Ser. Synergeffcs 1985, 29, 75-85. (H74) Kaul, David J.; Wolf, Eduardo E. J. Cafal. 1985, 93(2). 321-330. (H75) Kiss, Janos T.; Gonralez, Richard D. Ind. Eng. Chern. Prod. Res. Dev. 1985, 24(2), 216-219. (H76) Barshad, Yoav; Gularl, Erdogan J. 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1OOR


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Catal. 1988, 97, 248-251. (1108) Goodwin, J. G., Jr.; Lester, J. E.; Marceiin, G . ; Mitchell, S. F. ACS Symp. Ser. 1985, No. 288, 87-78. (1109) Forni, Lucio; Viscardi, Carlo F.; Oiiva, Cesare J. Catal. 1986, 97, 469-479. (1110) Forni, Lucio; Viscardi, Carlo F. J. Catal. 1988, 97, 460-492. (1111) Lechert, H.; Schweitzer, W. Zeolites 1985, 427-434. (I 112) Hiiierova, Eva; Lopez, Rafael; Maternova, Jindriska; Peter, Rudolf; Zdrazii, Mirosiav Collect. Czech. Chem. Commun. 1984, 49(1), 29-38. (1113) Bautista, F. M.; Campeio, J. M.; Garcia, A.; Luna, D.; Marinas, J. M. J. Colloid Interface Sci. 1986, 712(1), 79-66. (I1 14) Rajaram, Raj R.; Sermon, Paul A. J. Chem. Soc., faraday Trans. 1 1985, 87(11), 2593-2603. (1115) Hail, Peter G.; Hann, Richard A.; Heaton, Philip; Rosseinsky, David R. J . Chem. SOC.,Faraday Trans. 11985, 87(1), 69-82. (1116) Gishti, K.; Iannibeiio, A.; Marengo, S.; Moreiii, G.; Tittareiii, P. Appl. Catal. 1984, 72(3), 381-393. (1117) Stach, H.; Lohse, U.; Thamm, H.; Schirmer, W. Zeolites 1986, 6(2), 74-90. (1118) Janchen, J.; Stach, H. Zeolites 1985, 5(1), 57-59. ( I 119) Dzhigit, 0. M.; Kiseiev, A. V. (the late); Rachmanova, T. A. Zeolites 1984, 4(4), 389-397. (1120) Ruthven, D. M.; Goddard, M. Zedites 1988, 6(4), 275-282. (1121) Hwu, F. S.; Hightower, J. W. Prepr.-Am. Chem. SOC.,Div. Pet. Chem. 1984, 29(4), 1033-1037. (1122) Occeiii, M. L.; Innes, R. A.; Hwu, F. S. S.;Hightower, J. W. Appl. Catal. 1985, 14(1-3), 69-62. (1123) Choudhary, V. R.; Singh, A. P. Zeolites 1986, 6(3), 206-208. (I 124) Inomata, Makoto; Yamada, Masatoshi; Okada, Sanae; Niwa, Miki; Murakami, Yuichi J. Catal. 1988, 700, 264-269. (1125) Suzuki, Isao; Oki, Shoichi; Namba, Seitaro J. Catal. 1988, 100, 219-227. (1126) Shields. Joan E.; Loweii, S. J. Colloid Interface Sci. 1985, 703, 226-229. (1127) Shields, J. E.; Loweii, S. Powder Technol. 1985. 41, 269-271. (1128) toor, 1. A.; Lee, H. H. AIChE J. 1985, 37(12), 1939-1946. (1129) Niwa, Miki; Inagaki, Shinji; Murakami, Yuichi J. Phys. Chem. 1985, 89, 2550-2555. (1130) Niwa, Miki; Inagaki, Shinji; Murakami, Yuichi J. Phys. Chem. 1985, 89(16). 3869-3872. (1131) Pieters, W. J. M.; Venero, A. F. Catalysis on the Energy Scene 1984, 155-1 63. ANALYTICAL CHEMISTRY, VOL. 59, NO. 12, JUNE 15, 1987

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CATALYST CHARACTERIZATION (1132) McEnangy, B.; Masters, K. J. Thermochim. Acta 1984,82, 81-102. (1133) Hacskaylo, John J.; LeVan, M. Douglas Langmuir 1985, 7 , 97-100. (1134) Hope, A. T. J.; Catlow, C. R. A.; Leng, C. A,; Adams, C. J. Zeolites 1985,297-306. (1135) Gravelle, Pierre C. Thermochim. Acta 1985,96(2), 365-376. (I 136) Busca, Guido; Rossi, Pier Francesco; Lorenzelll, Vlncenzo; Benalssa, Mohammed; Travert, Josette; Lavalley, Jean-Claude J. fhys. Chem. 1985,89, 5433-5439. (1137) Stradella, Luigi; Vogliolo. Gianfranco Z . fhys. Chem. 1983, 737(1), 99-1 10. (1138) Stradella, L.; Peliuettl, E. Thermochim. Acta 1985,85, 19-22. (1139) Stradella, L.; Pellzzettl, E. J. Mol. Catal. 1984,26, 105-115. (1140) Stradella, L.; Pelizzettl, E. J. Mol. Catal. 1988,35, 221-226. Pankratiev, Yu. D.; Kuznetsov, 8. (1141) Efremov, A. A.; Bakhmutova, N. I.; N., React. Kinet. Catal. Lett. 1985,28(1), 103-110. (I 142) Fubinl, Bice; Giamello, Elio; Guglielminotti, Eugenlo; Zecchina, Adriano J. Mol.-Catal. 1985,32(2), 219-237. (1143) Ostrovskii, V. E.; Dyatlov, A. A., Kinet. Catal. 1984,25(5), 11971204; CA 707(26): 236167q. (1144) Ostrovskii. V. E.; Dyatlov, A. A,, Kinet. Catal. 1984, Vol. 25, 760-913. (1145) Fubini, B.; Bolis, V.; Giamello, E. Thermochlm. Acta 1985, 85, 23-26. (1146) Giamello, E.; Fubini, B.; Lawo, P. Appl. Catal. 1986,27(1). 133-147. (1147) Palfi, S.: Llsowski, W.; Smutek, M.; Cerny,, S. J. Catal. 1984,88(2). 300-312. (1148) Goncharuk, V. V.; Karakhim, S. A.; Pankrat’ev, Yu. D.; Balabanova, 0. P.: Oleinik, L. M. React. Kinet. Catal. Lett. 1985, 27(1), 163-166. (1149) Ostrovskii, V. E.; Medvedkova, E. A. Kinet. Catal. 1985, 28(6), 1433-1438; CA 704(23): 206634). (1150) Giamello, E.; Fubini, B.; Lauro, P.; Bossi, A. J. Catal. 1984,8 7 , 443-45 . .. . - I. . (1151) Tournayan, L.; Auroux, A.; Charcosset, H.; Szymanski, R. Adsorpt. Sci. Techno/. 1985,2(2), 55-68.

OTHERTECHNIQUES (JI) Bianchi, D.; Joly, J. P. Spectra 2000 1985, 707, 19-22; CA 703(8): 63938~. (J2) Ashton, A. G.; Dwyer, J.; Elliott, I.S.; Ftch, F. R.; Qin, G.; Greenwood, M.; Speakman, J. R o c . Int. Zeolite Conf., 6th 1984,704-716. (J3) Liu, W.; Tsong, T. T. Surf. Sci. 1986, 785(1), L26-L30. (J4) Ai. C. F.; Tsong, T. T. J. Chem. fhys. 1984,87(6), 2845-2854. (J5) Cocke, D. L.; Abend, G.; Block, J. H. Langmulr 1985, 7(4), 507-509. (J6) Kruse, Norbert; Abend, Guenter; Block, Jochen H. Chem.-Ing.-Tech. 1984,56(8), 610-611; CA 707(19): 1704779. (J7) Koudelka, M.; Monnier, A.; Sanchez, J.; Augustynski, J. J. Mol. Catal. 1984,25, 295-305. (J8) Spichiger-Ulmann, M.; Monnier, A.; Koudelka, M.; Augustynski, J. ACS Symp. Ser. 1988,No. 298, 212-227. (J9) Goboeloes, S.; Wu, Q.; Delmon, 8. Appl. Catal. 1984, 73(1), 89-100. (JIO) Vordonis, L.; Koutsoukos, P. G.; Lycourghiotls. A. Langmu/r 1988,2(3), 281-283. (J11) Mulay, L. N.; Pannaparayil, Thomas ACS Symp. Ser. 1985,No. 288, 498-517. (J12) Philllps, J.: Chen, Y.; Dumesic, J. A. ACS Symp. Ser. 1985,No. 288, 5 16-533. (J13) Johnston, D. C.; Silbemagel, 8. G.; Daage, M.; Chianeill, R. R. frepr.Am. Chem. Soc., Dlv. Pet. Chem. 1985,30(1), 206-212. (J14) Candy, J. P.; Perrlchon, V. J. Catal. 1984,89(1), 93-99. (J15) Purdue, G. E.; Williams. R . W. X-Ray Spectrom. 1985, 74(3), in3-inR .--. (J16) LaBrecque, J. J.; Rosales, P. A.; Marcano, E. J. Radioanal. Nucl. Chem. 1985,89(2), 455-463. (J17) Fabec, J. L.; Ruschak, M. L. At. Spectrosc. 1984, 5(4), 142-145. (J18) Carrion, N.; Llanos, A.; Benzo, 2.; Fraile, R. At. Spectrosc. 1988,

.--

712). 52-55. -- - 1-11

(J19) Lazaro Boza, Fernando; Luque de Castro Maria Dolores; Valcarcel Cases, M i u e l Analyst 1984, 709(3), 333-337. (J20) Hwang, J. M.; Tsung, J. C.; Chen. Y. M. J. Chin. Chem. SOC.1985, 32(4), 405-410. (J21) Maspoch, S.; Blanco, M.; Cerda, V.. Analyst 1988, 777(1). 89-72. (J22) Yarnane, Takeshi; Nozawa, Yasuhiko Bunseki Kagaku 1984. 33(12), 652-656; CA 7O2(16): 142309a. (J23) Zhou, Zhixian; Wang, Ling; Huang, Ling; Shen, Junying Huaxue Shfi 1985, 7(1), 9-10, 19; CA 103(14): 115193C. (J24) Perez Pont, M. L.; Sanchez, M. J.; Brlto, F.; Garcia Montelongo. F. An. Ou/m., Ser. B 1985,87(2), 245-247. (J25) Lazareva. V. I.; Lazarev, A. I.Zavod. Lab. 1985, 57(12), 1-5; CA 704(14): 122110~. (J26) Nakagawa. Toshiyuki; Doi, Kunio; Otomo. Makoto AnalVst 1985, 770(4), 387-390. . (J27) Zhou, Mingcheng; Yang, Guifa; Wang, Lixing, Huaxue Shfi 1985, 7(2). 102-105; CA 703(14): 1 1 5 2 0 0 ~

102R


(J26) Katarni, Takeo; Hayakawa, Tornokuni; Furukawa. Masamichi; Shibata, Shozo Bunmki Kagaku 1984,33(12), 678-678; CA 702(16): 1424100. (J29) Nakanishl, Tsutomu; Otomo, Makoto Anal. Sci. 1985, 7(2), 161-164. (J30) Rosales, Daniel: Gomez Ariza, Jose L.; Asuero, Agustln G. Analyst 1986, 7 7 7(4), 449-453. (J31) Franclsco Ortega, A.; Garcia Montelongo, F. Quim. Anal. 1985,4(4), 441-446. (J32) Singh, A. K.; Roy, Bani, Singh, R. P. J. Indian Chem. SOC. 1985, 62(4), 316-318. (J33) Ramdas, Subramanlam; Thomas, John M.; Betteridge, P. W.; Cheetham, Anthony K.; Davles, E. K. Angew Chem., Int. Ed. Engl. 1984,23, 671-679. (J34) Wright, Paul A.; Thomas, John M.; Cheetham, Anthony K.; Nowak, Andreas K. Nature 1985,378,611-614. (J35) W a r d , Willlam A., I11 Science 1985,227, 917-923.

MULTIPLE TECHNIQUES (KI) Hofmann, H. Appl. Catal. 19M, 75(1), 79-87. (K2) Riekert, L. Appl. Catal. 1985, 75(1), 89-102. (K3) Burch, R. Catalysis 1985, 7, 149-96. (K4) Davis, S. Mark; Somorjai, Gabor A. Bull. SOC. Chim. Fr. 1985,(3), 271-287. (K5) Bhatti, Asif S.;Dollimore, David Lab. Pract. 1984,33(6), 88-92. (K6) Haller, Gary L., Appl. Surf. Sci. 1985,20(4), 351-381. (K7) Fierro, Jose L. G.; Garcia de la Banda, Juan F. Catal. Rev.-Sci. Eng. 1988, 28(2-3), 265-333. (K8) Mortier, Wilfred J.; Schoonheydt, Robert A. frog. Solid State Chem. 1985, 76(1-2), 125. (K9) Dewing. J.; Spencer, M. S.; Whittam, T. V. Catal. Rev.-Sci. Eng. 1985,27(3). 461-514. (K10) Scholten, J. J. F.; Pljpers. A. P.; Hustings, A. M. L. Catal. Rev.-Sci. Eng. 1985. 27(1), 151-206. (K11) Gonzalez, Richard D. Appl. Surf. Scl. 1984, 79(1-4), 181-199. (K12) Kock, A. J. H. M.; -us, J. W. Rog. Swf. Scl. 1985,20(3), 165-272. (K13) Tanabe, Kozo Mater, Chem. Phys. 1985, 73(3-4), 347-364. (K14) Segawa, Koichi; Kinoshtta, Makio; Tanaka, Shinichi, Hyomen 1988, 24(1), 1-14; CA 704(16): 136661q. (K1.5) Ghosh. Ashim K.: Kydd, Ronald A. Catal. Rev.-Sci. €no. 1985, 27(4), 539-589. (K16) Sant, B. R.; Rao, s. B.; Rao, J. R.; Thakur, R. S.; ParIda, K. M. J . Sei. Ind. Res. 1984,43(10), 542-569. (K17) Goodall, Brian L. MMI Ress Syhp. Ser. 1983,4, 355-378. (K18) Yeager, Ernest; Scherson, Danlel A.; Fierro, Cristian A. ACS Symp. Ser. 1985,No. 288,535-549. (K19) Che, M.; Bonnevlot, L.; Louis, C.; Kermarec, M. Mater. Chem. fhys. 1985, 73(3-4), 201-220. (K20) Ermakov, Yu. I.Usp. Khim. 1988, 53(3), 499-556; CA 704(22): 193939k. (K21) Topsoe, Henrik; Candia, Roberto; ’Topsoe, Nan Yu; Clausen, Bjerne S. Bull. SOC.Chim. Belg. 1984,93(8-9), 783-808. (K22) Garreau, F. B.; Toulhoat, H.; Kasztelan, S.; Paulus, R. Polyhedron 1988,5(1-2), 211-217. (K23) Kantschews, M.; Delanmy, F.; Jezlorowski, H.; Delgado, E.; Eder, S.; Ertl, G.; Knoezinger, H. J. Catal. 1984, 87(2), 482-496. (K24) Scholle, K. F. M. G. J.; Veeman, W. S.; Frenken, P.; Van der Velden, G. P. M. Appl. Catal. 1985, 77(2), 233-259. (K25) Vdrine, Jacques C.; Auroux, Allne; Coudurler, Gisele ACS Symp. Ser. 1984,No. 248,253-273. (K26) Tebassi, L.; Sayarl, A.; Ghorbel, A.; Dufaux, M.; Naccache, C. J. Mol. Catal. 1984,25, 397-408; CA 701(19): 17044%. (K27) Andersson, Arne; Andersson, S. Lars T., ACS Symp. Ser. 1985,No. 279, 121-142. (K28) Garbassi, F.; Bart, J. C. J.; Montino, F.; Petrini, G. Appl. Catal. 1985, 16(3), 271-287. (K29) Collette, H.; Maroie, S.;Riga, J.; Verbist, J. J.; Gabellca, Z.; Nagy, J. B.; Derouane, E. G. J. Catal. 1986,98(2), 326-334. (K30) Zakl, M. I.; Fouad, N. E.; Leyrer, J.: Knoezinger, H. Appl. Catal. 1986, 21 12). 359-377 (K31) ‘Hanuza, J.; Jezowska-Trzebiatowska, B.; Oganowski, W. J. Mol. Catal. 1985.29(1). 109-143. (K32) Bondarev; Yu. M.; Chabarakada, T.; Koslova, N. E.; NikAin, V. V.; Komolova, L. P.; Mardashev, Yu. S.; Shishkin, Yu. L. Appl. Catal. 1985, 75(2), 227-233. (K33) Jiang Xuanzhen; Stevenson, Scott A,; Dumesic, J. A,; Kelly, Thomas F.; Casper, Richard J. J. Phys. Chem. 1984,88(25), 6191-6198. (K34) Aika, Kenichi; Yamaguchl, Takeshi; Onishi, Takaharu, Appl. Catal. 1986, 23(1), 129-137. (K35) Rojas, D.; Bussiere, P.; Dalmon, J. A,; Choplin, A,; Basset, J. M.; Olivier, D. Surf. Sci. 1985, 756(1). 516-529. (K36) Yamamda. Makoto; Iwasawa, Yasuhiro Nippon Kagaku Kaishi 1984, (6), 1042-1049; CA 707(6): 44046C. (K37) Chowdhry, U.; Ferretti, A.; Firment, L. E.; Machlels, C. J.; Ohuchi, F.; Sleight, A. W.; Staley, R. H. Appl. Surf. Sci. 1984, 79(1-4), 360-372.

Catalyst characterization - American Chemical Society

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