Effect of mild re-oxidation treatments with CO2 on the chemisorption capability of a Pt/CeO2 catalyst reduced at 500°C

By combining FTIR spectroscopy of chemisorbed CO and HRTEM, we have studied the evolution undergone by the metal chemisorption capability and nanostructural properties of a Pt/CeO2 catalyst reduced at increasing temperatures from 200 to 500 degreesC, As revealed by the nu (CO) integrated absorption data on Pt, a progressive metal deactivation is observed. The analysis of the HRTEM micrographs allows us to exclude metal sintering, decoration, and Pt-Ce alloying phenomena as the likely origin of the observed effect, If the catalyst reduced at 500 degreesC is further heated under CO2 (300 Torr), at a very mild temperature, 200 degreesC, its chemisorption capability is partly recovered. This regeneration effect is interpreted as due to the Pt-assisted CO2 re-oxidation of the ceria support with inherent chemisorption of the resulting CO on the metal microcrystals. These observations are consistent with the model recently proposed by our laboratory on the nature of the strong metal-support interaction phenomena occurring in NM/CeO2 catalysts. (C) 2001 Academic Press.