Plasma-Enabled Direct Methane-to-Methanol Conversion on Zeolite-Confined Copper-Oxo Clusters: Insight into Vibrational Excitation and Radical-Mediated Process

Selective one-step conversion of methane (CH4) to methanol (CH3OH) remains a grand challenge in catalysis, constrained by the trade-off between C─H bond activation and product overoxidation. Here, we integrate density functional theory (DFT) calculations with plasma-catalytic experiments to investigate direct CH4-to-CH3OH conversion using H2O as the sole oxidant on CuxOy clusters within MOR zeolite, compared to the CuO(111) surface. We show that C─H bond activation proceeds preferentially via homolytic H-abstraction on zeolite-confined CuxOy clusters, with Cu3O3/MOR exhibiting a low activation barrier of only 0.21 eV, more than three times lower than that on CuO(111). Vibrational mode-specificity analysis shows that the C─H stretching modes couple most effectively on higher-barrier surfaces. Importantly, we demonstrate that plasma-generated radical intermediates (CH3·, H·, OH·) reshape the reaction thermodynamics, with the Gibbs free energy shifting from endothermic (+1.13 eV) to exothermic (–3.21 eV and –8.25 eV), enabling pathways inaccessible under thermal conditions. Experimentally, Cu/MOR catalysts prepared by ion exchange, which favor well-dispersed zeolite-confined Cu-oxo sites, achieve the highest CH3OH production rate (0.26 mmol/h) at low plasma power (6.5 W), outperforming catalysts prepared by wetness impregnation. This work bridges Cu-oxo site topology, vibrational mode specificity, and radical-mediated thermodynamics, offering valuable insights for plasma-catalytic selective CH4-to-CH3OH conversion.