(583e) Kinetic Studies On Au and Pt Catalysts Supported On Model Al2O3 and TiO2 for the WGS Reaction
The water-gas shift reaction (WGSR), CO + H2O → CO2 + H2 plays an important role in hydrogen generation and purification by CO removal. Our kinetic analysis of Pt/Al2O3, Au/Al2O3 and Au/TiO2 catalysts suggests that the WGSR rate scales with the total number of Pt surface atoms, whereas the rate scales primarily with perimeter Au atoms for Au/Al2O3 catalysts and, as reported in a separate paper, with coordinatively unsaturated corner Au atoms for Au/TiO2 catalysts. To determine the rate as a function of particle size, model supports with simple geometry and no porosity were used. Precise particle size distributions could then be obtained by TEM since all of the metal is exposed on the surface of the support.
The WGS rate for Pt/Al2O3 and Pt/TiO2 catalysts was found to have the form A exp (-85(kJ/mole)/RT) [CO]^0.1[H2O]^0.9[H2]^-0.6[CO2]^0. However, the rate expression for Au/Al2O3 and Au/TiO2 catalysts was found to be different from that for Pt catalysts with lower apparent activation energy at 10-50 kJ/mole, a higher order with respect to CO of 0.8 and a variable order with respect to H2O ranging from -0.3 to 0.8 and depending on the Au particle size and the support. Mechanistic interpretation of the rate data and descriptors for the catalytic activity will be discussed.