Role and Evolution of Nanoparticle Structure and Chemical State during the Oxidation of NO over Size- and Shape-Controlled Pt/γ- Al2O3 Catalysts under Operando Conditions

摘要

The structure and chemical state of size- selected Pt nanoparticles (NPs) supported on γ-Al2O3 were studied during the oxidation of NO using X-ray absorption near-edge spectroscopy and extended X-ray absorption ?ne- structure spectroscopy measurements under operando con- ditions. The data revealed the formation of PtO_x species in the course of the reaction that remained present at the maximum temperature studied, 350 °C. The PtO_x species were found in all samples, but those with the smallest NPs showed the highest degree of oxidation. Moreover, NO-induced nano- particle redispersion was observed at temperatures below 150 °C for all catalysts studied. Catalytic tests showed activity toward the oxidation of NO for all samples. Nevertheless, the catalyst with the smallest NPs was found to be the least active, which is explained by a more extensive formation of PtO_x species in this catalyst and their detrimental contribution to the oxidation of NO.