Evidence for Weakly Bound Oxygen on Ceria Films

Abstract

Temperature-programmed desorption (TPD) has been used to compare the O2 desorption characteristics of a thin film of ceria prepared by vapor deposition on an α-Al2O3(0001) substrate with that of a CeO2(111) surface. On CeO2(111), there is no substantial desorption of O2 below ∼1300 K, while a low-temperature state, between 800 and 1250 K, was observed from the ceria film. Reexposure of the ceria film to O2 above 600 K repopulated this desorption feature, showing that adsorption−desorption cycles did not alter the morphology of the film. By adding Rh to the ceria film and then measuring the reaction of adsorbed CO on the Rh, it was demonstrated that this low-temperature feature is responsible for the oxidation of CO during TPD. The implications of these results for understanding the oxygen storage function of ceria-supported catalysts are discussed.