Unveiling the Role of Copper Valence States in Enhancing the Catalytic Performance of Copper-Modified ZSM-5 for Direct Methane Conversion

The conversion of methane (CH4) to methanol (CH3OH) under mild conditions remains a significant challenge in catalysis. In this study, we introduce a method to adjust the surface valence states of copper species in Cu-ZSM-5 catalysts by annealing under different atmospheres (N2, air, and H2). Among these, the 10% Cu-ZSM-5 catalyst calcined in H2showed outstanding performance, achieving a methanol productivity of 8.08 mmol/(gcat·h) and 91% selectivity at 70 °C and 3 MPa using H2O2as the oxidant. Comprehensive characterization revealed that H2annealing optimized the Cu surface to a lower valence state (predominantly Cu+), enhancing CH4adsorption and promoting H2O2activation to generate ·OH and ·CH3radicals, which drive selective CH3OH formation. In situ DRIFTS and radical trapping experiments further confirmed the critical role of Cu+in facilitating C-H bond cleavage and suppressing overoxidation.