4148
J . Phys. Chem. 1992, 96, 4148-4151
seems to be a weak interaction between the organic radical and some other species, probably zeolite impurities. This is clearly not detected in the Pd/L signal due to its significantly higher intensity. To have a rough estimate of the actual polypyrrole content in our zeolitic materials, a portion of the loaded Pd/L was evacuated at 373 K for 1 h and then heated at 923 K for another hour under 1 atm of pure 0,in the same vacuum line used for oxygen chemisorption. The glass system was equipped with a Baratron pressure transducer and a cold microtrap held at 150 K. After calcination, all organic carbon is assumed to be collected in the trap as CO, while excess O2can be totally evacuated from the adsorption line. Using this method, we determined the polymer formed in the zeolite to be 73 f 15% of the total amount of pyrrole initially present during the loading step. The large inaccuracy arises mainly from the fact that we do not know whether or not the organic nitrogen had also been retained in the cold trap. Nevertheless, it indicates that our monomer/metal ratios in the zeolite are roughly 1.5-2.5. Several implications of the above results are worth discussing. The standard Sn4+/Sn2+redox potential, Eo(Sn), is 0.16 V and in principle would not be sufficient to cause the oxidative polymerization of pyrrole to occur. One possibility would be that the redox potential of the Sn pair is significantly increased by the zeolite environment. It was mentioned above that thiophene oligomers within the Na-&zeolite cavities were synthesized by Caspar et al.9 These authors reported that the redox potential of this zeolite (in its sodium form) with respect to the saturated calomel electrode had been found to be about 1.6 V, high enough to induce thiophene polymerization. An alternative explanation would be that the small SnO, oxide clusters not only experience a perturbation in their redox properties induced by the host but also act as catalytic sites for oxidation of pyrrole by oxygen during the drying step, which may hold for the oxygen-covered Pd crystallites in the Pd/L catalyst as well. We choose the latter
since the pyrrole/metal loading ratio was found to be larger than 1.5 for the 0,-activated Pd/L catalyst, above the value of one required for the formation of a long polypyrrole chain. It should be noted that only in the extreme case of very short chain oligomer formation, Le., dimers or trimers, the reaction might still be stoichiometric. However, some fraction of dimers and trimers should be expected to diffuse out of the zeolite pores upon solvent extraction, but this is not what our infrared-extraction results indicate in the case of pyrrole adsorption reaction on the two catalysts. For example, it is possible to actually load a narrow-pore zeolite such as ZSM-5 with thiophene trimers in liquid media.9 In addition, the absence of hyperfine structure that we observe in Figure 3 has also been associated with the formation of longchain polymer^.^,^^ We conclude that rather high molecular weight species are formed catalytically by the supported particles on L zeolite. A number of questions still arise regarding the macroscopic properties of these composite materials as well as the chemical nature of the polymerization process and its role in determining the polymer (oligomer) chain length. Although it can be speculated that either “creeping” of short oligomer chains along the channels or oxygen spillover from active sites would provide the necessary mobility for reaction completion, the very modest temperatures used during the loading-drying steps do not seem, in principle, to allow such simple interpretations. Further work is needed to clarify the above-mentioned ideas. Acknowledgment. We are grateful to Prof. T. Randolph for the ESR measurements and his assistance concerning the interpretation of spectra. Partial support by the Office of Basic Sciences, DOE, and beam time a t the Cornell High Energy Synchrotron Source (C2 station) are also acknowledged. (18) Ramamurthy, V.; Caspar, J. V.; Corbin, D. R. J . Am. Chem. SOC. 1991, 113, 590.
Molecular Structures of M20 (M = B, AI, Ga) Suboxides. Bent or Linear? Jerzy Leszczyiiski* and Jdzef S. Kwiatkowskit Department of Chemistry, Jackson State University, Jackson, Mississippi 3921 7 (Received: January 31, 1992; In Final Form: April 13, 1992)
The molecular structures and properties of the B20,AI20, and Ga20 suboxides were studied by the ab initio method at the HF, MP2, and CISD levels with the triple-{ valence basis set augmented by d-polarization functions. For all these species the linear conformers are the global minimum structures at the MP2/TZP level. The calculated bond distances, rotational constants, and harmonic vibrational frequencies are in a very good agreement with the available experimental data. Predicted by calculations, but still experimentally elusive, low-energy vibrational bands for the boron and gallium suboxides may be used for identification of the studied species in further experiments.
Introduction There has been increasing interest in molecular structure and properties of the group I11 oxides. Boron oxides were studied recently as the products of boron interactions with water in the gas phase and in argon matrix isolation experiment^.'-^ Similar experiments were carried out with Al.4 Likewise, technological importance of aluminum oxides as products of the oxidation reactions stimulated numerous experimental studies on these species.5-8 For example, simple diatomic A10 was detected in different high-temperature sources such as stellar spectra and also in vapors over heated A1203.9J0 Additionally, aluminum oxides are important elements of coal fly and volcanic ashes. Furthermore, an application of metal oxides in the semiconductor industry ‘Permanent address: Institute of Physics, N. Copernicus University, 87100 Torui. Poland.
has stimulated research on matrix reactions of molecular oxygen and ozone with aluminum, gallium, indium, and thallium atoms.’-’’ In spite of a number of experimental and theoretical ~
~~
~
~~~~
~~~~
(1) Gole, J. L.; Pace, S . A. J. Phys. Chem. 1981, 85, 2651. (2) Jeong, G. H.; Boucher, R.; Klabunde, K. J. J . Am. Chem. SOC.1990, 112, 3332. (3) Andrews, L.; Burkholder, T. R. J . Phys. Chem. 1991, 95, 8544. (4) Oblath, S. B.; Gole, J. L. J . Chem. Phys. 1979, 70, 581. (5) Snelson, A. J. Phys. Chem. 1970, 74, 2574. (6) (a) Makowiecki, D. M.; Lynch, D. A., Jr.; Carlson, K. D. J . Phys. Chem. 1971, 75, 1963. (b) Lynch, D. A,, Jr.; Zehe, M.J.; Carlson, K. D. J . Phys. Chem. 1974, 78, 236. (7) Srebrennikov, L. V.; Osin, S . B.; Maltsev, A. A. J. Mol. Srrucr. 1982, 81, 25. (8) Sonchlik, S. M.; Andrews, L.; Carlson, K. D. J . Phys. Chem. 1983,87, 2004. (9) Babcock, H. D. Asrrophys. J . 1945, 102, 154. (10) Lindsay, D.; Gole, J. J . Chem. Phys. 1977, 66, 3886.
0022-365419212096-4148$03.00/0 0 1992 American Chemical Society
Letters
The Journal of Physical Chemistry, Vol. 96, No. 11, 1992 4149
data, the molecular structure and assignments of vibrational spectra of suboxide molecules M 2 0 (M = B, Al, Ga) are still controversial. Very recently, on the basis of the FTIR studies on a boron atom-water molecule reaction with its products trapped in solid argon, Andrews and Burkholder3 identified a new BOB molecule which they predicted to be slightly bent; however, they did not rule out the linear structure for this species. Interestingly, ab initio HartreeFock (HF) calculations with minimal basis set predicted a linear structure for B20.I2 Although a number of experimental and theoretical papers on A120 structure and properties have been published, assignments of the molecular geometry even for this species are not unique. Older experimental IR studies favor strongly the bent structure,6J3 but very recent fluorescence excitation and resolved emission experimentsI4 as well as ab initio studies at the H F l e ~ e l ~ ~ - I ’ predicted a linear, centrosymmetric structure for this molecule in its lowest electronic state. Recent calculations at the HF/631G* level by Boldyrev and SchleyerI*reported the existence of a local minimum bent conformer with an A1-O-A1 apex angle of 78.2O, higher in energy by 393 kl/mol than the global minimum linear species. The same paper revealed the MP2/6-31G* parameters for the linear A120 conformer. The experimental data for the Ga20 molecule is scarce. Studies on matrix reaction of O2with Ga atoms identifed gallium suboxide based on a very weak band at 823 cm-I.” Also, the presence of indium suboxide 1n20 was detected in the similar experiments carried out with In.” Recently we examined the molecular parameters and bonding properties of different boro, alo, and gallo hydrides at the H F 1 e ~ e l . l ~The present study was initiated to determine molecular structures and harmonic vibrational frequencies of the three suboxides molecules B20, A120, and G a 2 0 using ab initio Hartree-Fock and post-Hartree-Fock methods. We also explored a performance of the two post-HF techniques, extensively used MP2 theory and more expensive CISD approximation in prediction of the molecular parameters for the studied suboxides. Our results confirm that all the studied species in their ground state adopt the linear structures and also lighten a shadow on experimental observations of their bent configurations. Theoretical molecular parameters, harmonic vibrational frequencies, and intensities as well as rotational constants are reported to assist further experimental studies on the M 2 0 species. Method Ab initio LCAO-MO method was used to study the title species.20 To obtain reliable data, a large, triple valence basis set with polarization functions (TZP) was applied in our calculations. The Pople’s 6-3 1 lG* basis set was used for B and 021a and that of McLean-Chandler for Al,Zlb while Huzinaga’s partially uncontracted [433111/43111/4*] basis set supplemented with a set of 6 d-polarization functions (c = 0.207) was implemented for gallium.22 Anticipating the importance of the electron cor(1 1) Zehe, M. J.; Lynch, D. A., Jr.; Kelsall, B. J.; Carlson, K. D. J . Phys. Chem. 1979,83, 656. (12) Shillady, D.; Ginn, H.; Jones, L.; unpublished data, quoted in ref 3. (13) Linevsky, M. J.; White, D.; Mann, D. E. J . Chem. Phys. 1964, 41, 542. (14) Cai, M.; Carter, C. C.; Miller, T. A,; Bondybey, V. E. J. Chem. Phys. 1991, 95, 73. (15) Wagner, E. L. Theor. Chim. Acta 1974, 32, 295. (16) Salomonik, V. G.;Sazonova, I. G. Zh. Neorg. Khim. 1985,30, 1939. (17) Masip, J.; Clotet, A.; Ricart, J. M.; Illas, F.; Rubio, J. Chem. Phys. Left. 1988, 144, 373. (18) Boldyrev, A. I.; Schleyer, P. v. R. J. Am. Chem. Soc. 1991,113,9045. (19) (a) Lammertsma, K.; Leszczynski, J. J. Chem. Soc., Chem. Commun. 1989, 1005. (b) Lammertsma, K.; Leszczynski, J. J . Phys. Chem. 1990, 94, 2807. (c) Ibid. 1990.94, 5543. (d) Leszczynski, J.; Lammertsma, K. J . Phys. Chem. 1991, 95, 3941. (20) For an introduction to the methods employed see, for example: Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Inirio Molecular Orbital Theory; Wiley: New York, 1986. (21) (a) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J . Chem. Phys. 1980, 72, 650. (b) McLean, A. D.; Chandler, G.S. J . Chem. Phys. 1980, 72, 5639.
TABLE I: Predicted Molecular Parameters of M2’% (M = “B, *‘AI, 69Ga) IiB2 1 6 0 linear (bent)
quantitp
26A12160 linear (bent) SCF Level 169.89 180.0‘
69Ga2160 linea@ (bent) 171.89 (178.50) 180.OC(179.94) od (10-3)
r(M0) LMOM
130.96 180.OC
P
Od
Od
A
0.0 13383.915 -124.199783
0.0 0.0 3244.838 1240.834 (1 150.640) -558.821 751 -3917.875542 (-3917.880 301)
B EscF
r(M0) LMOM P
A
B
PcF EMP2
r(M0) LMOM
MP2 Level 172.28 180.95 132.93 (132.97) 180.OC 180.OC 180.OC(170.12) Od (0.184) Od Od 0.0 0.0 0.0 12 989.715 3155.220 1119.728 -124.199090 -558.821 138 -3917.879749 (-1 24.199 03 1) -124.561 760 -559.378 197 -3918.298958 (-124.561 757) 132.03 180.OC
CISD Level 170.73 180.OC
179.33 180.W
P
Od
Od
Od
A B EsCF EMP2
0.0 13 167.150 -124.199 573 -124.561 627 -124.554 182
0.0
0.0
3212.894 -558.821 672 -559.377 956 -559.336507
1140.049 -3917.880238 -3918.298 732 -3918.264429
fils’
“Bond lengths r in nanometers, bond angles L in degrees, dipole moments p in debye, rotational constants A and B = C in megahertz. For this optimized structure the negative value of v2 (degenerate) wavenumber is predicted. Constrained. Consequence of assumption on linearity of a molecule.
relation energy contributions on predicted structures on properties of the studied suboxides, we calculated the geometrical parameters and vibrational frequencies not only at the H F but also at two different post-HF levels. The optimizations of molecular geome t r i e ~were ~ ~ carried out for the linear and bent conformations at the H F and the second-order Molller-Plesset perturbation theory (MPZ(ful1)) approximation^.^^ All optimized structures were checked by an analysis of harmonic vibrational frequencies obtained from diagonalization of force constant matrices. Additionally, geometry optimizations at the CI level with all singlet and doublet substitutions (CISD (full)) were carried out for the linear species. However, due to the limitations in computer resources, vibrational frequencies were not calculated at this level. All calculations reported were performed with the GAUSSIAN 90 program.25 Results and Discussion A simplified MO model of triatomic AB2 group molecules predicts simple rules for a molecular shape of these species: molecules with 10 through 16 and 21 or 22 valence electrons are linear, those with 17 through 20 electrons are bent.26 The title M 2 0 suboxides with 12 valence electrons belong to the first class. However, experimental IR studies in argon matrix predicted B 2 0 molecule to be bent3 with the valence angle of BOB being equal (22) Huzinaga, S.; Andzelm, J.; Klobukowski, M.; Radzio-Andzelm, E.; Sakai, Y.; Tatewaki, H. Gaussian Basis Sets for Molecular Orbiral Calculations; Elsevier: New York, 1984. (23) Schlegel, H. B. J . Compur. Chem. 1982, 3, 314. (24) Moiler, C.; Plesset, M. S. Phys. Rev. 1934, 46, 618. (25) Frisch, M. J.; Head-Gordon, M.; Truck, G. W.; Foreman, J. B.; Schlegel, H. B.; Raghavachari, K.; Robb, M.; Binkley, J. S.; Gonzales, C.; DeFrees, D. J.; Fox, D. J.; Whiteside, H. B.; Seeger, R.; Melius, C. F.; Baker, J.; Martin, L.; Kahn, L. R.; Stewart, J. J. P.; Topiol, S.; Pople, J. A. GAUSSIAN 90, Revision H; Gaussian, Inc.: Pittsburgh, PA, 1990. (26) Gimarc, B. M. Molecular Srrucrure and Bonding; Academic Press: New York, 1979.
4150 The Journal of Physical Chemistry, Vol. 96, No. 11, 1992
Letters
TABLE II: Predicted and Observed IR Wavenumben (u, a“)and Absolute Intensities (km/mol, in Parentheses) of ‘lBZ160,nAl,’”O,
and
69ca2160
calcd
SCF u(A) linear
MP2 v(A)
exptl‘
linear
bent
V
1117 (0) 87 (12) 1554 (1122)
1043 (0) 23 (12) 1456 (1124)
1046 (1) 22 (12) 1451 (1108)
1420.5
550 (0) 138 (0.03) 1060 (736)
517 (0) 81 (0.4) 1001 (661)
525 99 993
300 (0) 52 (2) 854 (827)
823
379 177i 1092
bent
323 (0) 100 (2) 911 (883)
“Experimental data taken from ref 3 for B 2 0 (in solid argon), from ref 14 for AI20 (laser excitation spectra of jet cooled A120 in the gas phase), and from ref 11 for G a 2 0 (in solid argon)
to 163 f 10’. On the other hand, as is indicated by the experimental claims of existence of A120in two different conformations bent or linear,8J3J4~27J8 identification of molecular structures of the title suboxides by IR studies in inert matrixes may be troublesome. Both possible conformers bent (C, symmetry) and linear (Dmhsymmetry) are characterized by three different absorption bands. Although for the linear species under study there are four vibrational modes, two lowest energy (degenerated) modes are of the T symmetry, resulting in three distinct bands which may be recorded by the IR experiment. Furthermore, all three vibrational frequencies were observed only for the A120 molecule, while for the B and Ga suboxides the highest energy bands were recorded exclusively. Our theoretical predictions of molecular structures, rotational constants, and dipole moments of the three title species are summarized in Table I. We carried out geometry optimizations for both the bent and linear types of conformers at the HF and MP2 levels. Compared with the heavier analogues, a distinctive attribute of boron suboxide should be noticed. Only the linear conformer is a minimum structure on the B 2 0 potential energy surface (PES) at the HF level, and all attempts to obtain the bent species yielded the linear conformer. However, at the MP2 level both types of structures exist on the PES. The local minimum bent conformer is characterized by B-O-B angle of 170.1’ and B-O bond length of 1.3297 A, which is O.OOO4 A longer that in the global minimum linear species, regardless virtually the same calculated for both the conformers MP2 energies and harmonic vibrational frequencies (see Table 11). Further investigations including MP2 geometry optimization (only B-O distances with the BOB angle constrained at 172, 174, 176, and 178’) and vibrational frequency calculations, resulted in very similar MP2 energies, B-0 distances and vibrational frequencies for all the linear and bent structures. This result suggests existence of the very flat potential energy surface in the considered region rather than two distinct minima. In contrast, the bent conformers of A1 and Ga suboxides do not exist at the MP2 level. However for Ga20, the H F calculations yielded the bent minimum structure with the M U M bond angle 179.94’ close to (but not equal as in the analogous B,O case) 180°, but with the v3 vibrational frequency different from that of the linear species by as much as 182 cm-l. Unexpectedly, at the HF level, the linear GazO conformer is the second-order transition structure with the energy higher by 13 kJ/mol. This energy difference, noticeable at this level, explains the difference in the first vibrational frequencies (-177 vs 100 cm-’) for the linear and bent conformers, respectively, as well as decrease of the Ga-O bond length in the later species by as much as 0.0661 A. (27) (a) Ivanov, A. A.; Tolmachev, S. M.; Ezhov, Y. S.; Spiridinov, V. D.; Rambidi, N. G. Zh. Srrukt. Khim. 1973, 14, 917. (b) Tolmachev, S . M.; Rambidi, N. G. High Temp. Sci. 1973, 5, 385. (c) Also see Chase, M. W., Jr.; Curnutt, J. L.; McDonald, R. A.; Syverud, A. N. J. Phys. Chem. Rex Data 1978, 7 , 793. (28) Jacox, M. E. J. Phys. Chem. Ref. Data 1988, 17, 269.
At the MP2 level only linear Conformers of AI and Ga suboxides exist. All geometry optimizations a t this level yielded linear species. These observations and the existence of the linear global minimum B 2 0 a t the MP2 level enable additional, expensive geometry optimizations at the CISD level only for the linear species. There are some interesting features of the calculated molecular parameters. The B-O and A 1 4 bond distances at the HF approximation are shorter about 1.5% than the correspondin distances calculated at the MP2 level (1.3293 and 1.7228 respectively), although the analogous difference amounts to 5.3% for the linear G a p species. However, a linear G a 2 0 conformer is the second-order transition structure at the H F approximation and by comparison of the HF Ga-O distance of the minimumenergy bent structure, with that calculated for the linear gallium suboxide at the MP2 level (1.8095 A), one obtains a difference which amounts to 1.4%. The calculated M-O bond lengths at the CISD approximation are between HF and MP2 data being shorter than the corresponding MP2 distances by 0.7% (B-0) and 0.9% (Al-0 and Ga-O). Experimental bond distances which are known only for the A120 compound range from 1.64 to 1.72 Experimental rotational constant of A120 (3165.627 M H Z ) ~is~accurate J~ predicted by the MP2 data (3155.220 MHz), that at the CISD level being slightly too large (3212.894 MHz). On the basis of the obtained res& and our previous studies29 on small selenium species a t the H F and MP2 levels using the similar bases sets to those applied in our current calculations, we believe that both the MP2 and CISD post-HF methods accurately predict molecular parameters and properties of the studied suboxides. However, a small difference (less than 1%) between CISD and MP2 data and a slightly better correlation with the available experimental data justified, especially for geometry predictions of larger molecular systems, the choice of the much more economical MP2 level. Table I1 shows the remarkable agreement between predicted and experimental vibrational frequencies. It should be noticed that no scaling factors were used for the reported theoretical frequencies. We observe improvement of the calculated MP2/ TZP vibrational frequencies for AlzO to compare with those reported by Boldyrev and SchleyerI8 at the MP2/6-31G* level (513, 90, and 988 cm-’, respectively). The accuracy of the presented data is even more pronounced when one relates the calculated and experimental shift of vibrational frequencies upon isotopic substitutions (Table 111). In this case the differences between predicted and experimental parameters are not larger than 3 cm-I, the theoretical data being smaller in all cases. It is obvious that one should be able to use predicted vibrational frequencies for B 2 0 and G a 2 0 suboxides to identify their ex-
1,
A.14927328
(29) (a) Leszczyfiski, J.; Hale, B.; Lszczyplska, D. In?.J . Quantum Chem. 1991, QCS25, 451. (b) Leszczyfiski, J.; Kwiatkowski, J. S.; Leszczyfiska, D.
Chem. Phys. Left.,in press.
J. Phys. Chem. 1992, 96,4151-4154 TABLE III: Observed' and Calculated (in Parentheses) Shifts (cm-I) of Antisymmetric Stretching Fundamental Vibrations in B20,A120, and Ga20 upon Isotopic Substitution 10B180lOB 44 (47)
llB160llB 29 (30)
lOBl60IOB + IIBIBOIIB lOB16011B 75 (78) 14 (14)
-
loBl8OllB 58 (61)
27~12160
27~12180 44-45 (44) 69Ga18069Ga 40 (44)
71Ga 16071Ga ? (2)
69Gal6069Ga + 7 lGa18071Ga 69Ga 16071Ga ? (45) ? (1)
69Gal SO7 lGa ? (45)
Experimental data taken from ref 3 for B20, from ref 7 for AI20, and from ref 11 for Ga20. Data for B 2 0 and A120 in argon matrix and for Ga,O in nitrogen matrix.
perimentally still elusive v 1 and v2 low-energy bands, which according to our calculations are much less intensive than recorded v3 modes.
Conclusions The linear conformers of the title suboxides are the global minima on the MP2/TZP potential energy surfaces. It is also
4151
evident that the excellent agreement between theoretical and available experimental data strongly suggests that the all studied species are linear. However, the potential energy surfaces near linear structures are flat, and also near-linear conformations may be adopted (particularly in inert gas matrices) which might cause additional problems with the experimental characterizations of these species. The H F geometry optimizations failed in the case of the Ga20 linear species, and we found that the post-HF procedures are necessary for the reliable characterizationsof the studied systems. The comparison between calculated at the MP2/TZP level molecular parameters, vibrational frequencies, rotational constants, and available experimental data shows a very good agreement. We conclude that the calculated parameters may be used for identification of the studied species in further experiments (e.g., among different products observed in reactions of the third group elements with water or oxygen). Acknowledgment. This work was supported by the National Science Foundation Grant RII-8902064 and by the LBL/ JSU/AGMEF/DOE consortium. The Mississippi Center for Supercomputing Research and the Minnesota Supercomputer Institute are acknowledged for generous allotment of computer time. We appreciate the referee's valuable comments.
Deuterium Nuclear Magnetic Resonance Characterization of Supported Rhodium Catalysts: Effect of the Support Tsong-huei Chang, Cheu Pyeng Cheng,* and Chuin-tih Yeh* Department of Chemistry, National Tsing Hua University, Hsin-Chu, Taiwan 30043 (Received: February 7 , 1992; In Final Form: April 6, 1992)
Metal-support interactions were investigated by 2H NMR for deuterium adsorbed on Rh supported on S O 2 ,A1203,Ti02 (in a non-SMSI state), NaY zeolite, and MgO. Two types of adsorbed species, Dm and Dw, with distinct chemical shifts irrespective of supports, were detected on all supports except that Dw was not detected on Rh/AI2O3. The molar fractions of Dm and Dw are support dependent as well as deuterium overpressure dependent. The line widths of Dm and Dw are also support dependent. These results indicate that the major effects of the support are the number of active sites and the motions of Dm and Dw.
Various spectral techniques have been used to probe the interIntroduction actions between metals and supports. Slichter'~l~-'~ and Duncan's Since heterogeneous catalytic reactions occur on the surfaces groups'"18 used I3CNMR to study CO adsorbed on Rh supported of catalysts, it is desirable to have catalysts with a large surface by Ti02, Alz03, S O z , and zeolite. 19VtNMR has also been used area so that rates of reactions are enhanced. For this reason, most industrial metallic catalysts are prepared by dispersing active and usually expensive metals into small crystallites on supports with (7) Kawalski, J.; van der Lee, G.; Ponec, V. Appl. Caral. 1985, 19, 423. (8) Kuznetsov, V. L.;Romanenko, V. V.; Mudrakovskii, I. L.; Matikhin, large surface area. Although the supports were originally conV. M.; Schmachkov, V. A.; Yermakow, Y. I. Proc. 8rh Inr. Congr. Caral. sidered to be chemically inert, evidence of support and metal Berlin, 1984; Vol. 5 , p 3. interactions which affect the activity and selectivity of the catalytic (9) Underwood, R. P.; Bell, A. T. Appl. Caral. 1986, 21, 157. reactions has gradually accumulated. For example, extensive (10) Arkawa, H.; Takekuchi, K.; Makchuzaki, T.; Sugi, Y. Chem. Lett. 1984, 1607. studies of CO hydrogenation over Rh have established that the (11) Van? Blik. H. F.: Vis. J. C.: Huizinaa, - T.: Prins. R. ADPI. .. Caral. activity and selectivity of catalysts are strongly influenced by the 1985, 19, 405. nature of s u p p ~ r t s and l ~ by the size of the rhodium p a r t i ~ l e s . ~ ~ * ~ ~ (12) Wang, P. K.; Ansermet, J. P.; Rudaz, S. L.;Wang, Z.; Shore, S.; (1) Ichikawa, M. Bull. Chem. Soc. Jpn. 1978, 51, 2273. (2) Ichikawa, M.; Shikakura, K. Proc. 7rh Inr. Cong. Caral. Tokyo, Part 9,1980, p 925. (3) Katzer. J. R.; Sleight, A. W.; Gajardo, P.; Micheal, J. B.; Gleason, E. F.; McMillan, S. Faraday Discuss. Chem. Soc. 1981, 72, 121. (4) Solymosi, F.; Tombacz, I.; Koszta, J. J . Caral. 1985, 95, 578. ( 5 ) van der Lee,G.; Schuller. B.; Post, H.; Favre, T. L. F.; Ponec, V. J. Caral. 1986, 98, 522. (6) Gilbooley, K.; Jackson, S.D.; Rigby, S. Appl. Caral. 1986, 21, 349.
Slichter. C . P.: Sinfelt. J. H. Science 1986. 234. 35. (13) Makowka, C. D.; Slichter, C. P. Phys. Reo. B 1985, 31, 5663. (14) Rudaz, S. L.;Ansermet, J. P.; Wang, P. K.; Slichter, C. P.; Sinfelt, J. M. Phys. Rev. Lerr. 1985, 54, 71. (15) Makowka, C. D.; Slichter, C. P. Phys. Reo. Lerr. 1982, 49, 379. (16) Duncan, T. M.; Yates, Jr. J. T.; Vaughan, R. W. J . Chem. Phys. 1980, 73, 975. (17) Duncan, T. M.; Root, T. W. J. Phys. Chem. 1988, 92, 4426. (18) Duncan, T. M.; Yates, Jr. J. T.; Vaughan, R. W. J . Chem. Phys. 1979, 71, 3129.
0022-3654/92/2096-4151%03.00/0 0 1992 American Chemical Society
