Effect of Mild Re-oxidation Treatments with CO_2 on the Chemisorption Capability of a Pt/CeO_2 Catalyst Reduced at 500 deg C

摘要

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/CeO_2 catalyst reduced at increasing temperatures from 200 to 500°C. As revealed by the Vco 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 soo°C is further heated under CO_2 (300 Torr), at a very mild temperature, 200°C, its chemisorption capability is partly recovered. This regeneration effect is interpreted as due to the Pt-assisted CO_2 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/CeO_2 catalysts.