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-suppo rted Pd particles have been studied by temperature-programmed desorpti on (TPD) using molecular beam techniques. The results of size effect s tudies show clearly different surface properties of bulk metal and sup ported clusters. Surprising effect of partical CO dissociation was obs erved on small Pd particles deposited on gamma-alumina, prepared by th ermal oxidation of aluminum, and not on Pd/alpha-alumina model catalys ts. The activation energy of CO desorption, E-d, was determined as a f unction of particle size. The E-d decreased with decreasing particle s ize. The CO and oxygen sticking probability measurements indicated the CO and oxygen diffusion over the support. It was shown that the oxyge n adsorption capacity and the reactivity of alumina-supported catalyst s were higher than those of Pd(111).