Influence of surface structure on the mechanism of CO adsorption and catalytic oxidation on palladium

The adsorption and oxidation of carbon monoxide on small alumina-supported Pd particles have been studied by temperature-programmed desorption (TPD) using molecular beam techniques. The results of size effect studies show clearly different surface properties of bulk metal and supported clusters. Surprising effect of partical CO dissociation was observed on small Pd particles deposited on γ-alumina, prepared by thermal oxidation of aluminum, and not on Pd/α-alumina model catalysts. The activation energy of CO desorption, Ed, was determined as a function of particle size. The Ed decreased with decreasing particle size. The CO and oxygen sticking probability measurements indicated the CO and oxygen diffusion over the support. It was shown that the oxygen adsorption capacity and the reactivity of alumina-supported catalysts were higher than those of Pd(111).