Robust Microwave Catalytic Oxidative Coupling of Methane over Mn2O3-TiO2-Na2WO4/SiO2+SiC
Oxidative coupling of methane (OCM) is a promising route for direct conversion of methane to C2–C3 hydrocarbons, but conventional thermal catalysis suffers from insufficient conversion and selectivity. Here, we report a novel Mn2O3-TiO2-Na2WO4/SiO2+SiC microwave catalyst prepared by ball-milling, which enables efficient OCM under microwave irradiation. At 700 °C, the microwave catalytic reaction mode (MCRM) achieves a CH4 conversion of 26.6%, a C2–C3 selectivity of 76.5%, and a C2–C3 yield of 20.4%, significantly outperforming the conventional reaction mode (CRM) under identical conditions (12.3%, 61.9%, and 7.5%, respectively). The catalyst exhibits stable performance for 20 h in MCRM, maintaining CH4 conversion above 25% and C2–C3 selectivity above 76%. Characterization (XRD, XPS, O2-TPD, Raman) reveals that calcination promotes Mn–Ti interaction, increasing peroxy species and lattice oxygen (Oγ), which enhance reactivity and selectivity. Notably, microwave irradiation reduces the apparent activation energy from 173 kJ/mol (CRM) to 27.5 kJ/mol, facilitating free radical coupling and suppressing deep oxidation. These findings provide a low-temperature, energy-efficient strategy for methane valorization, contributing to sustainable chemical manufacturing.