J . Phys. Chem. 1988, 92, 2270-2275
2270
No strong micellar growth is indicated in the entire micellar region. From QLS and electron microscopy a micelle-to-vesicletransition was observed. The MO-NaTC-water system shows important analogies with lecithin-bile salt-water systems,27~66*67 but there are also important differences. In both cases the isotropic solution phase region has a shape such that mixed micellar solutions on dilution with water may not remain in the single phase region but pass into the two-phase region of isotropic solution lamellar LC phase. This is understood from the large monomeric solubility of bile salt (and the low one of M O or lecithin) making the aggregates richer in the other (bilayer-forming) component of the aggregate. On dilution into the two-phase region, conditions are given for kinetic stabilization of unilamellar vesicles which form in both types of systems. For lecithin systems? vesicle formation is preceded by a major micellar growth into disk-shaped aggregates while for the monoolein system micelle growth is small. (Note the coexistence of large vesicles and small mixed micelles.) Furthermore, for lecithin systems coexistence of mixed micelles and simple bile salt micelles is very pronounced while for the MO-NaTC case mixed-simple micelle coexistence is much less significant. Of course, the phenomena of micelle growth and coexistence are interrelated: it is only with micelle growth that there can be micelles with different curvature and thus different relative energetic conditions for lipid and bile salt and unequal partitioning. While the main reason for investigating bile salts and monoglycerides in aqueous solution is the physiological relevance as a good model system in studies of fat digestion and absorption in the intestine, it is also an interesting system in connection with attempts to understand amphiphilic systems in general.
+
Acknowledgment. We are indebted to Prof. Peter Stilbs and Dr. Roger Rymd6n for their very valuable help with the selfdiffusion measurements. We are also very grateful to Dr. E. Wehrli for the electron microscopy studies, to Dr. Bodil Ericsson for the DSC measurements, and to Dr. Ali Khan for some 2H and 23Na N M R measurements. Prof. KBre Larsson, Prof. HBkan Wennerstrom, Dr. Olle Siiderman, Dr. Ali Khan, and Dr. Paivi Jokela are gratefully acknowledged for fruitful discussions, and Dr. Norman Mazer and Dr. Gordon Tiddy are thanked for their thorough and constructive criticism of the manuscript.
Appendix. Poisson-Boltzmann Calculations The Poisson-Boltzmann equation is used in this work to obtain the changes in the fraction of bound counterions and the surface composition for a lamellar liquid crystalline phase as the water content in the system is changed. For charged liquid crystalline systems, it is not possible to use a simple partition equilibrium
between free and bound counterions or between T C ions in a lamellar aggregate and T C ions in the water part, since the electrostatic potential at the surface of a lamellar aggregate is strongly dependent on factors such as water layer thickness and ion strength, factors not normally found in simple equilibrium equations. The equilibrium equation for binding of an ion to a site in a charged system may approximately be written as c b exp(-ze@,/kT) = KCf exp(-ze&/kT) (Al) where C, and Cf are the concentrations of bound and free ions, respectively, ze is the charge of the ion, k T is the Boltzmann factor, K is an equilibrium constant, and & - df is the potential difference between the bound site and the free site. (Equation A1 is slightly modified for voluminous ions such as T C and other amphiphilic molecules,7s but this effect will here be neglected.) The PB equation is used to calculate the electrostatic potential difference (bb - 4f,where & normally for a lamellar system is taken to be the potential in the water part at midpoint between two lamellar interface^.^^ For the MO-NaTC system the PB equation for 4, = 4 - 4f becomess7 ( d h / d ~ )=~2N,dT/w,[c+o (exp(-e4,/kT) - 1) + c-€ (exp(e4,/kT) - 111 (A2) where NAis Avogadro's number, cot, is the permittivity of water, and c, and c, are the concentrations of Na+ and TC- at midpoint between two lamellar aggregates. Equation A2 may be solved by using elliptic integrals,s7 but since this solution is rather cumbersome to use except in computer calculations, we will here only give an approximative solution valid when the TC- concentration in the water part is small. exp(-e$/kT) = 1 /cos2 (sx/L) ('43)
Pb = 1 - tan [s(l - 2A/dw)]/tan s
(A41
?repulsive = (1 - s/tan ~ ) ( - 2 a k T / e ) where s may be calculated from s tan s = -aedw/4cot,kT
(A51
iA6) a is here the surface charge density, and totr is the permittivity of water. Registry No. MO, 11 1-03-5; NaTC, 145-42-6. (73) Woodford, P.F. J . Lipid Res. 1969, 10, 539. (74) Sherrill, B. C.; Albright, J. G.; Dietschy, J. M. Biochim. Biophys. Acta 1973, 311, 261. (75) Jonsson, B.; Wennerstrom, H. J . Colloid Interface Sci. 1981,80, 482. (76) Persson, N.-0.; Wennerstrom, H.; Lindman, B. Acta Chem. Scand. 1973, 27, 1667. (77) Persson, N.-0.; Lindman, B. J . Phys. Chem. 1975, 79, 1410.
Preparation and Structural Characterization of an Unprotected Copper Sol Andrew C. Curtis, Daniel G. Duff, Peter P. Edwards,* David A. Jefferson,* Brian F. G. Johnson,* Angus I. Kirkland, and Andrew S. Wallace University Chemical Laboratory, Lensfield Road, Cambridge CB2 I E W, United Kingdom (Received: April 1, 1987; In Final Form: October 7 , 1987)
Colloidal particles of copper have been prepared in methanolic solution by the reduction of copper(I1) salts with hydrazine hydrate. Importantly, this synthesis does not require the presence of steric stabilizing agents. Structural characterization using transmission electron microscopy at atomic resolution revealed the presence of both multiply twinned and parallel twinned particle morphologies.
Introduction There have been several accounts of the preparation of copper sols by the reduction of aqueous copper(I1) salts in the presence of polymer protecting agents.'" There is also one report of the 0022-3654/88/2092-2270$01.50/0
formation of an unprotected copper dispersion by the reduction of an m " n i a c a l solution of coPPer(I1) oxide by hydrazine hY( 1 ) Gutbier, A. Z . Anorg. Chem. 1902, 32, 347.
0 1988 American Chemical Society
The Journal of Physical Chemistry. Vol. 92. No. 8. 1988 2211
An Unprotected Copper Sol IXIIKTOW
b FIpm 1. (a) Optical spenrum ofthe dcsp red colloidal solution. with a peak maximum at 560 nm. (b) Typical lowmagnificationTEM image, showing the range of panicle sizes. A measured particle size distribution is shown inset.
dratc and phosphorus in ether.' but no structural information regarding the nature of the particles in the sol has been published. In this paper we report the novel synthesis of a copper organosol, which does not require steric stabilizing agents. and in which the particle sizes have b x n determined by using transmission electron microscopy (TEM) and structures by extensive examination a t atomic resolution. The results of this work, which show both similarities and differences when compared to previous studies of evaporated gold and silver particles,8-'n are presented. (2) Saucr. E.;Stciner. D.Kolloid-Z. 1935. 72, 35. (3) Pawvasiliou. G . C.: Kokkinakis. T. 3. Phys. F 1974. 4. L67. (4) Hi&, H ; Wakabayarhi. H.: Komiyama. M. Chrm. Lrrr. 1983. 1047. ( 5 ) Hirai. H.; Wakabayarhi. H.: Komiyama. M. Bull. Chrm Sor. Jpn. 1986. 59, 367. (6) Thick. H.; YO" Levern.
H.S . J . Colloid Sci. 1965. 20.679. (7)Freundlich. H.; Steiner. D.3. Chem. Sm. 1937. 1081.
Experinentnl Section Copper(l1) acetate monohydrate (140 mg: Aldrich Chemical Co.; Gold label) in methanol (500 mL; Fisons: AR grade) was boiled under reflux in an atmosphere of nitrogen for 2 h. An aliquot (IO mL) of a solution of hydrazine hydrate (0.2 mL; BDH Chemicals Ltd.; AR grade) in deoxygenated methanol ( I 0 0 mL) was added to the refluxing mpper(l1) solution. with constant stirring. The resulting solution was cooled and transferred under argon to a controlled-atmosphere glovebox. where all further manipulations were performed. With this method unprotected cooDer sols in ethanol and orooan-2-01 and also wMvinvl. .. . pGiolidone) protected sols in solvents and acetonitrile have (8) Marks.
L. D.:Smith, D. J. 3. Mierarr. (Oxfor4 1983, 130. 249. (9)Marks. L. D.:Howic. A. N a v m (London) 1979.282, 196. ( I O ) Marks. L.D.: Howie.A.:Smith. D.ConJ Sw.-lnrt. P h p . 1980. No. 52,397.
2111 The Journal of Physical Chemistry. Vol. 92. No. 8. 1988
Curtis et al.
f"nenm
.
b
1 b
Flpm 2. (a) Optical rpstrum of the dark green colloidal solution. showing the shift in peak maximum. (b) Low-magnification TEM. clearly indicating the aggregation of particles.
been prepared. These will be the subject of a subsequent communication." Preliminary characterization of the sol by optical spectroscopy was carried out using a Pye-Unicam SP8800 ultravioletvisible spectrophotometer with I-cm stoppered quartz cells. Samples for transmission electron microscopy were prepared by placing a drop of the sol on a 3.05-mm copper grid coated with a thin amorphous carbon film and allowed to stand for I min. Excess solution was then removed by placing the grid on absorbent paper before it was placed in the specimen holder. The whole proces$ was carried out in an argon atmosphere. The microscope column was also flushed with argon before loading the sample. Initial TEM characterization at low magnification was carried out using a JEOL JEM-ZOOCX electron microscope operating (II)Cunir.A.C.:Duff.D.G.:Edwsrdi.P.P.:Jcffmon.D.A.:Johnmn.
B. F. G.:Kirkland. A. 1.:
Wallace. A. S.. manuscript in preparation.
at 200 kV in the side-entry configuration. a IO-" objective aperture being used to enhance image contrast. Particle size analysis was carried out by direct measurement from micrographs recorded a t a magnification of 1OOOOOX. For high-resolution examination, a modified JEOL J E M - 2 W X was used employing a new type of side-entry specimen stage, details of which have been given elsewhere.'z The objective lens characteristics (C, = O S 2 mm. C, = I .OS mm at 200 kV) were such that, at a focus slightly below the Scherzer position, an interpretable point resolution of 1.95 A was attainable with information extending out to at least 1.8 A. Under these circumstances only the II I I ) diffracted beams of copper could be incorporated into the image with their correct relative phase shifts. and consequently most images were recorded a t a defwus where both ( I I I1 and (200) (12) Jefferson. D.A,: Thomas. J. M.: Millward. G.R.: Truna. K.: Harriman. A,: Brydron. R. D. Nature (London) I9R6. 323.428.
An Unprotected Copper Sol
The Journal of Physical Chemistry. Vol. 92. No. 8. 1988 2213
EXTlEXTlCN
t0
1 53 5% 603 69 100 WViLEffiM I nm Fi- 3. Changa in the optical spectra upon limited oxidation, showing the shift in peak maximum from 560 to 640 nm. 450
a
beams were given the same phase shift by the objective lens. In such cases the contrast was reversed, and the atoms appeared as white dots in the image. Care was taken to ensure that the illumination system was correctly aligned." and astigmatism was corrected by observing the granularity of the amorphous carbon support film. Micrographs were recorded at magnifications of either ca. 475000X or 690000X. a series of pictures for each group of particles being taken with increments of ca. 300-A defocus between each. Owing to the small size of the particles, no attempt was made to orient individual particles into ( I I O ) orientations, suitable areas being located instead by a systematic screening of the specimen grid.
Results and Discussion Upon addition of the hydrazine hydrate to the bluegreen copper(l1) solution, the color immediately changed to yelloworange, darkening to a deep red over 10-20 s, this latter hue persisting indefinitely if the solution was not exposed to air. No noticeable scattering of light was observed, and a typical optical spectrum is illustrated in Figure la. The peak maximum at 560 nm is in good agreement with that predicted from the Mie thmry14 when applied to small spherical copper particles." Low-resolution T E M indicated a mean particle size of 135 A with a range of diameters from 30 to 300 A (Figure Ib). although if smaller volumes of solutions were used, with consequently more efficient mixing of reagents, these figures could be reduced to 75 and 30-1 50 A, respectively. When the specimens described above were exposed to air. the red color persisted for only a few seconds. changing first to brown and then rapidly to dark green, with the peak maximum in the optical spectrum being shifted to ca. 590 nm (Figure 2a). T E M showed this dark green wlution to consist of aggregates of particles (Figure 2b). possibly with some evidence of surface coating. Prolonged exposure to air produced a pale blue-green copper(I1) solution with no evidence of particulate matter. Limited exposure caused the peak maximum to be shifted to ca. 640 nm with an increase in extinction, after which the extinction fell. Figure 3 (13) Smith. D. J.: Burrill. L. A,: Woad. G. J. Olrmmicrormpy 1985. 16. 19. (14)
Mie. G.Ann. Phyr. (Leipzig) 1908.25. 377. S a also: Kcrker. M. The Scorrrring of Light ond orher Elmrerromc7gnrtir Radiation: Academic: New York. 1969. (15) Radrhcnko. I. S.:Fonkich. M. E. Opl. Spec~cosc.(Engl. Trawl.) 1969. 25. 118.
b
Approximately decehedral particle of copper. viewed down the fivefold symmetry axis. The boundaries between individual crystallites forming the decahedron are indicated. The buildup of Smaller randomly oriented crystallites around the edges of the main particle is clearly visible. (b) Smaller particle possessing an apparently pcrfect dccahedral morphology. Figure 4. (a)
illustrates the changes in the optical spectra that take place. High-resolution TEM studies of samples from the red solution indicated two basic types of copper particles. The predominant type was similar to the multiply twinned particles ( M T R ) observed in gold and silver prepared by vacuum-evaporationR."or by colloidal solution In this copper sample the larger M T R rarely showed ideal decahedral or icosahedral morphologies and generally exhibited considerable strain contrast at the twin boundaries. often -sing smaller crystallites around their edges. A typical example is shown in Figure 4a. For particles of less than 100-A diameter. the moroholoev -, was nearer the ideal case. A virtually perfect d&hedral example is shown in Figure 4b. with no visible strain contrast at the boundaries between individual cryStalliteS in
.
(16) Duff. D. G.; Curtis. A. C.: Edwards. P. P.: Jellcson. D. A,: Johnmn. B. F. G.: Kirkland. A. I.: Logan. D. E. A n ~ e w .Chem.. Inr. Ed. Enpi. 19117.
26. 676.
2214 The Journal of Physicul Chemistry. Vol. 92. No. 8. 1988
Curtis et al.
a
Figure 5. Particle of copper showing five parallel {II I)twin planes. all passing completely across the crystal. The electron beam is parallel to a ( I I O ) direction.
The second morphology of the larger particles was one in which parallel ( 1 I l l twin planes were observed, as shown in Figure 5. Although parallel twinned lamellae have previously been reported and analyzed in detail," the particles in this sample differ in that the twin planes are approximately evenly spaced a c r m the particle. If crystals could be found with a ( I IO) axis exactly parallel to the electron beam, no strain contrast was visible at these twin planes, which frequently disappeared under the influence of electron bombardment. The effect obwrved was always to reduce the number of twin planes rather than to rearrange them. If a specimen grid of the red sol was exposed to air, the same morphologies were still observed. but the particles were coated with an epitaxial layer as shown in Figure 6, parts a and b. Due to the very small dimensions of this region, its exact nature was impossible to identify, but optical diffractometry indicated that the fringe spacings corresponded to those of copper(1) oxide. This effect was also noted in the aggregated sol, where an apparently amorphous layer surrounded the metal/metal oxide particles. Small crystallites were frequently observed in this layer, and the crystallinity of the layer itself appeared to improve with prolonged exposure to the electron beam. Some evidence for the formation of small, uncoated copper particles (possibly resulting from the reduction of copper(1) oxide by the electron beam1*) was noted. Conclusions
The morphologies shown by colloidal copper suggest that a t least two nucleation and growth processes may be operative in the same sample. The observation of large, imperfect MTPs and smaller, perfect ones. as reponed for colloidal ~ i l v e r , ' ~ .suggest '~.~ (17)
(18)
Smith. D. J.; Marks. L. D.J . Cryst. Growth 1981. 54. 433. Long. N. J.; Petford-Long. A. K. Ultromirrosmpy 1986. 20. 151. Marks. L. D.;Howic. A. Nature (London) 1979. 282. 196.
(19) (20) Smith. D. J.; Marks. L. D. Philos. Mag. A 1981.44. 735.
b Figure 6. (a) Particle of copper from the dark green solution. showing parallel twins with a distinct increase in the ( I 1 II fringe spacing parallel l o the long axis of the crystal. Measurements indicate that these correspond to the ( I I I ] fringes a l Cu,O. (b) Second particle from the same sample. also showing parallel twins. but with a much Ius pronounced coating. although some surface features are clearly visible.
that nucleation may take place via a strained polytetrahedral core. The particles then grow by subsequent metallic packing around this core. The particles of Figure 4. parts a and b. are of the typc expected from previous studies on evaporated However. the presence of parallel twinned particles suggests that there are conditions under which polytetrahedral nucleation gives way to more conventional fcc-type nucleiz' and that the samples examined may be prepared under such conditions. Thus in this preparation neither the isotropic nor strong facetting models proposed by mark^^',^' are entirely appropriate. The destabilization and aggregation of the dispersion on exposure to air are thought to be due to the depletion of the negative {-potential c m " n to metal solsz6by surface oxidation. (21) Marks. L. D.; Smith. D.J. 3. C r p t . Growth 1981.54. 425. (22) Yang. C. Y.: Heincmann. K.: Yaeaman. M. J.; Popp. H.ThinSolid Films 1979.58, 163. (23) Uyeda. N.:Nishino. M.: Suito. E.J. Colloid Interface Sri. 1573.13. ,LA _I-.
(24) Marks. L. D. 1.C r y x Growth 1983, 61. 556. (25) Marks. L. D. Philos. Mag. A 1984. 49. 81.
J. Phys. Chem. 1988, 92, 2215-2282 Further work to ascertain the effects of chemical factors on the nucleation and growth of the copper particles is continuing, and attemPts are being made to elucidate the nature and type of the surfacks present on the various kinds of particles. If a ielationship does exist between the particle structure and surface type, (26) Frens, G.; Overbeek, J. Th. G. Kolloid Z . Z . Polym. 1969, 233,922.
2275
the importance of chemical control over preparation cannot be overemphasized in view of the catalytic significance of finely divided copper. __
Acknowledgment. We thank British Alcan, ICI, and Johnson Matthev for financial sumort. P.P.E. also thanks the Nuffield Foundation for the award of a fellowship. Registry No. Cu, 7440-50-8; hydrazine hydrate, 7803-57-8.
Surface Chemical Structures of V205-P205 Catalysts Atsushi Satsuma,* Atsushi Hattori, Akio Furuta,+Akira Miyamoto,*Tadashi Hattori, and Yuichi Murakami Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Chikusa- ku, Nagoya 464, Japan, and Kinu- ura Research Department, JGC Corporation, Sunosaki-cho, Handa. Aichi 475, Japan (Received: June 1 , 1987)
Surface chemical structures of V205-P205catalysts were investigated by using X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), temperature-programmed desorption (TPD)of NH3,infrared spectra of adsorbed NH3 and pyridine, and the NARP (nitric oxide-ammonia rectangular pulse) technique. The concentration of the surface V = O species remarkably increased with P2O5 content below P/V = 1.0, but it decreased on further addition of P205. The increase in the surface V=O species was attributed to the lower oxidation state of vanadium ions in the bulk of the V205-P205 catalysts. The addition of P2O5 increased the surface concentration and the strength of acid sites, which consist mostly of Brernsted acid sites and of a slight amount of Lewis acid sites. It was concluded that, at high P/V ratio, all of the surface V and P ions act as the active functional groups; all P ions form P-OH species having a function of Brernsted acid, and all V ions form the surface V=O species having a redox function.
Introduction V205-P205 catalysts are one of the most important catalysts in industry, especially in the selective oxidation of butane to maleic anhydride.' Addition of the P205to V 2 0 5greatly increases the selectivity of the maleic anhydride. Many investigations have been devoted to the identification of the catalytically active phase in the V205-P205system. p-VOP04, a-VOP04, (VO)2P207,p"phase, and B-phase are the ones to which high yield of maleic anhydride has been ascribed. Bordes and Courtine2 have related the high selectivity to the redox cycle between the p-VOP04 and (VO)2P207,while Matsuura, suggested a redox system between ar-VOPO, and (VO)2P207. Hodnett and Delmon4 suggested that the amount of p"-VOP04 phase and V4+ ions in bulk are the important factors for selective oxidation. Shimoda et aL5 and Moser et aL6 ascribed the high yield of maleic anhydride to (VO)2P207which stabilizes V4+ ions, and Trifird et al.7 to B-phase which also stabilizes V4+ ions. In any case, emphasis was placed on the presence of the phase containing V4+ ions. The crystalline phase of the catalyst has an effect on the catalytic properties, but it does less directly than the surface structures does. The catalytic properties directly depend on the structure of the catalyst surface, especially on the active sites. It has been said that the surface V=O species are the active sites of V2O5 catalysts in the oxidation of many substances.s The acidic properties are also said to play an important role in the determination of the catalytic properties in some oxidation rea c t i o n ~ . ~ , In ' ~ the case of the NO-NH3 reaction on V2O5, for example, acidic V-OH adsorbs NH,, and the surface V=O oxidatively abstracts a hydrogen atom to form N2. Thus, the active sites consist of two active functional groups: the surface V=O species and surface V-OH species." In this paper, we have investigated the changes in the active functional groups, Le., the changes of the surface V=O species JGC Corp. 'Present address: Department of Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University, Sakyo-ku, Kyoto 606, Japan
0022-3654/88/2092-2275$01.50/0
and the acid sites by the addition of P2O5 to V2O5, in order to describe the surface chemical structures of the V ~ O S - P ~catO~ (1) (a) Varma, R. L.; Saraf, D. N. Ind. Eng. Chem. Prod. Res. Deu. 1979, 18, 7. (b) Rylander, P. N. In Cafalysis Science & Technology; Anderson, J. R., Boudart, M., Eds.; Springer-Verlag: New York, 1983; Vol. 4, p 25. (c) Ai, M. J . Cafal. 1986,100, 336. (d) Garbassi, F.; Bart, J. C. J.; Tassinari, R.; Vlaic, G.; Lagarde, P. J . Catal. 1986, 98, 317. (2) Bordes. E.: Courtine. P. J . Catal. 1979. 57. 236. (3) Matsuura,~I. The 6ih Japan-Soviet Catalysis Seminar; 1981, 149. Proc. Inf. Congr. Catal., 8th 1984, 4, 473. (4) Hodnett, B. K.; Permanne, Ph.; Delmon, B. Appl. Catal. 1983,6, 231. Hodnett, B. K.; Delmon, B. Ibid. 1984, 9, 203. (5) Shimoda, T.; Okuhara, T.; Misono, M. Bull. Chem. SOC.Jpn. 1985, 58, 2163. (6) Moser, T. P.; Schrader, G. L. J . Cafal. 1985, 92, 216. (7) Poli, G.; Resta, I.; Ruggeri, 0.;TrifirB, F. Appl. Catal. 1981, I , 395. Centi, G.; Manenti, I.; Riva, A,; Trifir6, F. Ibid. 1984, 9, 177. Cavani, F.; Centi, G.; Trifir6, F. Ibid. 1984, 9, 191. (8) (a) Cole, D. J.; Cullis, C. F.; Hucknall, D. J. J . Chem. SOC.,Faraday Trans. 1 1976, 72, 2185. (b) Akimoto, M.; Usami, M.; Echigoya, E. Bull. Chem. SOC.Jpn. 1978,51, 2195. (c) Bond, G. C.; Sirkiny, A. J.; Parfitt, G. D. J . Catal. 1979, 57, 476. Bond, G. C.; Konig, P. Ibid. 1982, 77, 309. (d) Anpo, M.; Tanahashi, I.; Kubokawa, Y. J . Phys. Chem. 1980,84,3440. ( e ) Andersson, A.; Lundin, S . T. J . Cafal. 1979, 58, 383. Ibid. 1980, 65, 9. Jonson, B.; Rebenstorf, B.; Larsson, R.; Andersson, S. L. T.; Lundin, S. T. J . Chem. Soc., Faraday Trans. 1 1986,82,767. ( f ) Mori, K.; Inomata, M.; Miyamoto, A,; Murakami, Y. J . Phys. Chem. 1983,87,4560; J . Chem. SOC., Faraday Trans. 1 1984,80,2655. Mori, K.; Miyamoto, A.;f Murakami, Y. J . Phys. Chem. 1984,88,2735,2741,5232. Ibid. 1985,89,4265. (g) Tanaka, T.; Ooe, M.; Funabiki, T.; Yoshida, S. J. Chem. SOC.,Faraday Trans. 1 1986, 82, 35. Tanaka, T.; Tsuchitani, R.; Ooe, M.; Funabiki, T.; Yoshida, S. J . Phys. Chem. 1986, 90, 4905. (h) Hengstun, A. J.; Pranger, J.; HengstumNijhuis, S. M.; Ommen, J. G.; Gellings, P. J. J . Cafal. 1986, 201, 323. (9) (a) Arriagada, R.; Cid, R.; Villasefior, J.; Pecchi, G. Z . Phys. Chem. (Munich) 1983,138, 117. (b) Nowiiiska, K. Z . Phys. Chem. (Munich) 1982, 131, 101. (c) Miyata, H.; Nakagawa, Y.; Ono, T.; Kubokawa, Y. J . Chem. SOC.,Faraday Trans. I 1983, 79, 2343. (d) Ai, M. J . Catal. 1981, 71, 88. Ibid. 1982, 77, 279. Ibid. 1983, 83, 141; Proc. In?. Congr. Catal. 8th 1984, 5, 474. (10) Busca, G.; Centi, G.; Trifir6, F.; Lorenzelli, V J. Phys. Chem. 1986, 90, 1337. (1 1) Inomata, M.; Miyamoto, A,; Murakami, Y. J . Cafal. 1980.62, 140. Miyamoto, A,; Inomata, M.; Hattori, A,; Ui, T.; Murakami, Y . J. Mol. Catal. 1982, 16, 315
0 1988 American Chemical Society
