Metal-support interactions between Pt and thin film cerium oxide

The interaction between Pt and reduced or oxidized cerium oxide (CeOX) has been studied by CO TPD and core-level SXPS. Reduced CeOX strongly modifies the chemisorption of CO on the supported Pt. Two different modifications are evident depending on annealing temperature, If the sample is annealed to greater than 800 K, the amount of CO that adsorbs on the Pt at 150 K is dramatically reduced. In addition, annealing at elevated temperatures decreases the Pt XPS intensity significantly. These results suggest that, similar to Pt on reduced TiOX, the Pt is covered by the reduced CeOX at elevated temperatures. If freshly deposited Pt is annealed to 700 K or less before CO is adsorbed at 150 K, there is no decrease in the amount of CO that adsorbs. However, the CO desorption temperature is shifted to a much lower temperature compared to CO adsorbed on a Pt single crystal. This shift in the CO desorption temperature is ascribed to a weakening of the CO-Pt bond that results from an electronic interaction between the Pt and the reduced ceria. The behavior of Pt on CeOX is compared to the very different interaction between Rh and CeOX. The CO-Rh bond is strengthened on CeOX compared to Rh single crystals and there is an increase in the CO dissociation activity. Rh also shows no evidence of encapsulation when annealed to higher temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.