Evolution of surface and bulk structure of supported palladium nanoparticles by in situ X-ray absorption and infrared spectroscopies: Effect of temperature, CO and CH4 gas

Interaction of CO and CH4 with palladium is a relevant process in numerous catalytic reactions, which may induce structural changes in the metal affecting its catalytic properties This work establishes a systematic study of the evolution of the atomic and electronic structure in alumina-and carbon-supported palladium nanoparticles in presence of CO and CH4 gases at temperatures from 50 to 350 degrees C by a combination of in situ X-ray absorption and infrared spectroscopies. Immediate adsorption of CO molecules with formation of surface carbon deposits due to the disproportionation reaction occurs at low temperatures, while above 250 degrees C, active formation of bulk palladium carbide is observed. In CH4 the later process starts only at ca. 350 degrees C. Reduction of palladium and contraction of the Pd-Pd interatomic distances were observed with increasing temperature irrespective of the gas atmosphere, including the inert one, particle size and the type of support. For carbon supported samples formation of palladium carbide occurred above 200 degrees C due to the decomposition of the support.

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This study establishes a systematic investigation of the evolution of the atomic and electronic structure in alumina-and carbon-supported palladium nanoparticles in the presence of CO and CH4 gases. The immediate adsorption of CO molecules and the active formation of bulk palladium carbide were observed at different temperatures, while the latter process in CH4 started at a higher temperature. The reduction of palladium and the contraction of interatomic distances occurred with increasing temperature, regardless of the gas atmosphere, particle size, and support type. For carbon-supported samples, the formation of palladium carbide occurred above a certain temperature due to the decomposition of the support.