The Crucial Role of Oxidants in Steering the Selective Oxidation of Methane and Subsequent Reactions on Cu/CHA Zeolites

Cu-exchanged zeolites are crucial catalysts for activating small molecules toward value-added or environmentally benign products. This study investigates the oxidant-driven methane conversion over Cu/CHA, with a focus on the role of oxidants (N2O vs O2) in modulating catalytic performance and reaction mechanisms. Cu/CHA zeolites were prepared by ion exchange with Cu species primarily existing as highly dispersed isolated Cu2+ ions and partially paired Cu species, as confirmed by XAFS, HAADF-STEM, and NO adsorption FTIR spectroscopy. Comparative studies revealed distinct catalytic performance depending on the oxidant. Higher CH4 conversion and CH3OH selectivity were achieved in the N2O-driven system than in the O2 case. The possible reason was attributed to the monatomic oxygen generated on Cu sites by N2O decomposition, which cleaved the C–H bond of CH4, inserted an oxygen atom, and yielded methanol. With the low risk of overoxidation, methanol would be further converted to light olefins on the acid sites at appropriate temperatures. However, O2 as the oxidant enabled the formation of aggressive peroxo (O22–) intermediates, promoting overoxidation to CO2 and limiting methanol selectivity. The choice of oxidant greatly influences the reactivity and selectivity of Cu/CHA in methane conversion. This study demonstrates that optimizing oxidant-catalyst interactions is vital for enhancing methane functionalization.