Elucidation of the Active Phase in Pd‐Based Catalysts Supporting on Octahedral CeO 2 for Low‐Temperature Methane Oxidation

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Abstract
Pd catalysts supported on CeO 2 (Pd/CeO 2 ) are highly active towards lean methane combustion, and the catalytic behavior is substantially affected by the chemical property of surface palladium species. In this work, various Pd catalysts supported on octahedral‐CeO 2 (Pd/O‐CeO 2 ) were successfully prepared by redox interation‐engaged strategy. The oxidation state of palladium species was controlled by varying the calcination condition. X‐ray absorption characterization coupled with light‐off curves confirmed that the catalytic activity of relevant catalysts was closely related with the proportion of the metallic Pd and PdO species. Within limits, increasing Pd 0 /PdO ratio can bring superior catalytic behavior and the approximately equal ratio of interfacial hybrid Pd 0 /PdO phase exhibits the optimal catalytic activity. Importantly, in situ DRIFTS results demonstrated that the hybrid Pd 0 /PdO phase was recognized as the active site pair for lean methane oxidation, which is attributed to the fact that the metallic Pd 0 species can adsorb and dissociate methane molecules and then the resulting intermediate species further react with the active O* of PdO, which thereby promotes CH 4 activation.

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