Redox dynamics of platinum species on CeO2 during CO oxidation reaction

Abstract

Ceria supported platinum catalysts play an important role in exhaust emission catalysis. Because of the interactions between catalyst and reactants under complex reaction conditions, Pt species may exhibit dynamic structural changes as a function of the reactant pressure and reaction temperature, making it difficult to determine the structure-performance relationship. In this study, the chemical states and dynamics of several typical Pt species, including PtOx, Pt–O–Ce and reduced Pt nanoparticles (NPs), in CO oxidation reaction and their correlations with activity were explored. It was found that Pt–O–Ce species with strong Pt–O bonds remained in the ionic state during the light off reaction, while PtOx species that interacted weakly with CeO2 could be easily reduced to metallic Pt (Pt0), which also exhibited better activity due to the enhanced reducibility of the Pt NPs-CeO2 interface. Although the initial activity of the Pt/CeO2 catalyst can be improved through reduction with H2, the metallic Pt NPs, especially derived from the reduction of Pt–O–Ce dominated catalysts, can get reoxidized to the less active Ptn+–O–Ce (n = 2–δ) species during the reaction. A detailed in situ characterization revealed that the oxidation of metallic Pt NPs arises from oxygen reverse spillover from the CeO2 support. This study shows that understanding the reaction-driven structural dynamics of Pt species is essential for exploring the reaction mechanism and elucidating how the catalyst is activated and deactivated in the reaction.