Enhancement of dissociation by metal-support interaction: reaction of NO on Rh supported by ceria films of controlled oxidation state

Highly oriented thin films of cerium oxide with variable ratio of Ce³⁺/Ce⁴⁺ were grown on Ru(0 0 0 1) single crystal surface and loaded with a fixed, low coverage of Rh. The chemisorption of NO on the resulting model catalyst was studied by soft X-ray photoemission which yielded the relative quantities of N containing species on the surface as a function of temperature, and by thermal desorption which yielded the relative yields of NO and N₂ desorbed. It is found that the ability of the reduced Rh clusters to dissociate NO depends upon the oxidation state of the ceria upon which it is deposited, and for highly reduced ceria surfaces effectively 100% of Rh-adsorbed NO dissociates by 350 K. Possible causes of this surprising behavior are discussed.