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Abstract

BACKGROUND: Grand efforts have been recently devoted to the development of catalysts based on the excellent performance of Cu- and Fe-dependent enzymes in methanotrophic bacteria for the partial oxidation of methane to methanol under ambient conditions. As a continuation of the study on the stepwise manner for this conversion over zeolite-based catalysts, in this work, the effects of zeolite topology and activation temperature on the catalytic performance of Cu- and Fe-containing zeolites were investigated.

RESULTS: Cu species exchanged in the medium-pore zeolites (mordenite, ZSM-5, and ferrierite) afforded better methanol production, while large-pore zeolites (zeolite β and zeolite γ) were inappropriate to accommodate active Cu sites. Notably, Cu/silicalite-1 containing CuO species was also reactive to methane after the activation in O₂, yielding a minor methanol amount. Furthermore, the activity of Fe/mordenite towards the methanol in the O₂-assisted procedure was reported for the first time but with a much lower yield as compared to that of Cu/mordenite. The methanol yield over Cu/mordenite increased with the activation temperature because increasing the activation temperature favored the Cu-exchange degree with a higher priority at the side pockets as compared to the main channels of mordenite, as evidenced from infrared analysis.

CONCLUSION: The selective oxidation of methane to methanol by O₂ via a stepwise manner can be obtained over both ion-exchanged Cu species and well-dispersed CuO nanoparticles with better activity being recorded for the former. The activity of Cu-exchanged zeolites was considerably dependent on the zeolite topology and the charge-balancing position of the Cu²⁺ cations.