EVIDENCE FOR LOW-TEMPERATURE OXYGEN MIGRATION FROM CERIA TO RH

We have examined the structure and adsorption propertiesRh deposited on amorphous ceria films in ultrahigh vacuum. Following adsorption of CO on Rh/ceria, a significant fraction of the CO reacts to CO2 during temperature-programmed desorption (TPD), even for relatively large Rh particles. The extra oxygen is shown to come from the ceria, since the near-surface region can be depleted by multiple adsorption-desorption cycles and since additional oxygen can be brought out from the bulk ceria by high-temperature annealing. The adsorption of NO on Rh/ceria is alsoaffected in ways that suggest that the oxygen is migrating to thesurface of the Rh near room temperature. These results have important implications on the catalytic properties of Rh/ceria catalysts and help to explain the high activity of these catalysts for the water-gas-shift reaction. © 1993 Academic Press, Inc.