(99b) Evaluation of Low-Temperature Methane Oxidation Reaction over Pd Single-Atom Catalysts
AIChE Annual Meeting
2022 Annual Meeting
Catalysis and Reaction Engineering Division
Environmental Catalysis II: Fundamental Catalysis
Monday, November 14, 2022 - 12:50pm to 1:10pm
This work adopts flame spray pyrolysis, a high-temperature synthesis method, to stabilize Pd on CeO2 in different flame synthesis environments. The developed catalysts are tested for methane oxidation to elucidate Pd speciation and the reaction mechanism using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The 1 wt.% Pd/CeO2 catalyst synthesized in the oxidizing environment has a lower T50 and a higher methane oxidation rate than the reducing environment-synthesized catalyst. This is due to the atomically dispersed Pd2+ species formed on the oxidizing environment-synthesized catalyst compared to the highly dispersed Pdn+, Pd0, and Pd0 clusters formed on the reducing environment-synthesized catalysts. The in situ DRIFTS indicates that carbonate species at 1273 cm-1 and 1540 cm-1 increase during methane oxidation at 400 oC over the 1 wt.% Pd/CeO2 catalyst. Formate and C-H methyl species at 1353 cm-1 and 2966 cm-1 also increase during the reaction, whereas CH2 species at 1475 cm-1 decrease. These results indicate that the conversion of adsorbed CH2 species to carbonate and formate may be an essential elementary step in the methane oxidation reaction over the atomically dispersed Pd2+. In situ evaluation of the methane oxidation reaction will be extended to the low loading Pd/CeO2 catalyst. The insight from these results can be used to elucidate the detailed reaction mechanism of methane oxidation reaction over single-atom Pd/CeO2 catalysts.