Surface studies of model supported catalysts: NO adsorption on Rh/CeO2(001)

The adsorption and reaction of NO on a model catalyst composed of Rh supported on ceria has been studied. CeO2 films were grown epitaxially by laser ablation onto SrTiO3(001) substrates. X-ray diffraction and transmission electron microscopy indicate the films are single crystalline with (001) orientation. Comparison of experimental and computer simulated ion scattering distributions indicate that an annealed CeO2 surface is well ordered and is composed of both O and Ce terminated domains. Exposures to CO and H-2 at various temperatures had little or no effect upon the ceria. Photoemission from the Ce 4d levels exhibits complex features that differ between a sputtered and a fully oxidized surface. NO does not adsorb on the Rh free, fully oxidized surface, but does adsorb upon a sputter reduced surface. The thermally induced conversion from molecular NO to atomic N was measured by both N Is photoemission and x-ray absorption as a function of Rh coverage to determine substrate effects on Rh surface chemistry. Rh deposited on sputtered ceria is more active for NO decomposition and yields higher N-2 desorption temperatures than does Rh on the fully oxidized support. (C) 1997 American Vacuum Society.