Effects of metal-support interactions on the chemisorption of H2 and CO on Pd/SiO2 and Pd/La2O3

Abstract The adsorption of H 2 and CO was investigated on SiO 2 - and La 2 O 3 -supported Pd catalysts, and the structure of adsorbed CO was characterized by infrared spectroscopy. For each of the Pd SiO 2 catalysts, the ratio of adsorbed H atoms, or adsorbed CO, to surface Pd atoms is unity. The stoichiometry for atomic adsorption of H 2 on Pd La 2 O 3 is also unity, independent of Pd dispersion. By contrast, the adsorption stoichiometry for CO decreases linearly from 0.6 to 0 as the Pd dispersion decreased from 30 to 8%. The suppression of CO adsorption is attributed to patches of partially reduced support material, LaO x , transferred to the surface of the Pd crystallites during catalyst preparation. The fraction of the Pd crystallite surface covered by LaO x increases with Pd dispersion, in agreement with conclusions based on earlier XPS studies. Infrared studies indicate that the structures of CO adsorbed on Pd La 2 O 3 and Pd SiO 2 are similar, but that the strength of adsorption is weaker for Pd La 2 O 3 than for Pd SiO 2 . This is attributed to a weakening in the σ-bond component of the PdCO bond due to charge transfer from the LaO x patches to the Pd crystallites. The absence of any suppression of H 2 adsorption of Pd La 2 O 3 indicates that H 2 adsorption occurs both on the exposed Pd surface atoms as well as on the LaO x patches covering the balance of the surface Pd atoms.

[1]  A. Bradshaw,et al.  IR reflection-absorption spectroscopy of CO adsorbed on palladium , 1975 .

[2]  J. Geus,et al.  On the Role of Promotors in Pd Catalysts for Methanol Synthesis , 1982 .

[3]  V. Ponec,et al.  Synthesis gas reactions on Pd-catalysts , 1982 .

[4]  J. Dumesic,et al.  Evidence for slow uptake of hydrogen by titania-supported metal samples: consequences for estimating metallic surface areas , 1983 .

[5]  J. Clarke,et al.  Infrared spectra of carbon monoxide adsorbed on palladium , 1967 .

[6]  G. Kadinov,et al.  Infrared spectroscopic study of the interaction between carbon monoxide and hydrogen on supported palladium , 1982 .

[7]  S. C. Fung,et al.  Strong metal-support interactions: Occurrence among the binary oxides of groups IIA–VB , 1978 .

[8]  J. Freel.  Chemisorption on supported platinum: I. Evaluation of a pulse method , 1972 .

[9]  W. Sachtler,et al.  Infrared spectra of carbon monoxide adsorbed on supported palladium and palladium-silver alloys , 1974 .

[10]  A. Ortega,et al.  The adsorption of CO on Pd(100) studied by IR reflection absorption spectroscopy , 1982 .

[11]  M. Vannice,et al.  Determination of IR extinction coefficients for linear- and bridged-bonded carbon monoxide on supported palladium , 1981 .

[12]  S. C. Fung,et al.  Strong interactions in supported-metal catalysts. , 1981, Science.

[13]  M. L. Hair,et al.  Infrared spectroscopy in surface chemistry , 1967 .

[14]  M. Boudart.  Structure of metallic catalysts , 1978 .

[15]  M. Boudart,et al.  Solubility of hydrogen in small particles of palladium , 1975 .

[16]  Alexis T. Bell,et al.  An XPS study of metal-support interactions on Pd/SiO2 and Pd/La2O3 , 1984 .

[17]  R. Kokes,et al.  The infrared spectrum of carbon monoxide on reduced and oxidized palladium , 1975 .

[18]  D. Resasco,et al.  A model of metal-oxide support interaction for Rh on TiO2 , 1983 .

[19]  V. Ponec,et al.  On the selectivity of palladium catalysts in synthesis gas reactions , 1983 .

[20]  W. A. Pliskin,et al.  The Effect of Surface Coverage on the Spectra of Chemisorbed CO. , 1956 .

[21]  S. Moon,et al.  The effect of SMSI (strong metal-support interaction) behavior on CO adsorption and hydrogenation on Pd catalysts: II. Kinetic behavior in the methanation reaction , 1981 .

[22]  J. Dumesic,et al.  Metal-support interactions between iron and titania for catalysts prepared by thermal decomposition of iron pentacarbonyl and by impregnation , 1983 .

[23]  J. Lunsford,et al.  Methane and methanol synthesis over supported palladium catalysts , 1982 .

[24]  M. Rosynek,et al.  Preparation and characterization of catalytic lanthanum oxide , 1977 .

[25]  M. Poutsma,et al.  Selective formation of methanol from synthesis gas over palladium catalysts , 1978 .

[26]  G. Schrader,et al.  In Situ FT-IR Spectroscopy of the Adsorption of CO on Methanol Catalysts , 1981 .

[27]  T. Onishi,et al.  Selective hydrogenation of carbon monoxide on palladium catalysts , 1981 .

[28]  V. Ponec.  On Some Real and Apparent Carrier Effects in Catalysis by Metals , 1982 .

[29]  P. Mériaudeau,et al.  Further Investigation on Metal-Support Interaction: TiO2, CeO2, SiO2 Supported Platinum Catalysts , 1982 .

[30]  H. L. Gruber.  An Adsorption Flow Method for Specific Metal Surface Area Determination. , 1962 .

[31]  S. C. Fung,et al.  Strong metal-support interactions. Group 8 noble metals supported on titanium dioxide , 1978 .

[32]  P. Aben.  Palladium areas in supported catalystsDetermination of palladium surface areas in supported catalysts by means of hydrogen chemisorption , 1968 .

[33]  M. Rosynek,et al.  Infrared study of carbon dioxide adsorption on lanthanum sesquioxide and trihydroxide , 1977 .

[34]  M. Modell,et al.  Palladium-catalyzed carbon monoxide oxidation. Catalyst "break-in" phenomenon , 1970 .

[35]  A. Bradshaw,et al.  The chemisorption of carbon monoxide on palladium single crystal surfaces: IR spectroscopic evidence for localised site adsorption , 1978 .

[36]  K. Nakamoto.  Infrared and Raman Spectra of Inorganic and Coordination Compounds , 1978 .

[37]  Alexis T. Bell,et al.  EFFECTS OF METAL-SUPPORT INTERACTIONS ON THE SYNTHESIS OF METHANOL OVER PALLADIUM , 1981 .