Solar-energy-driven conversion of oxygen-bearing low-concentration coal mine methane into methanol on full-spectrum-responsive WO3−x catalysts

Abstract

Sunlight-driven photocatalysis is regarded as a promising strategy for direct conversion of methane in low concentration coal mine methane (LC-CMM) to value-added methanol, yet remains a grand challenge to efficiently activate and convert methane. Herein, WO3−x nanosheets with gradient concentration of oxygen vacancy were synthesized and firstly served as full-spectrum responsive catalysts for transformation of LC-CMM to methanol at ambient conditions. Defect-rich WO3−x-N2.0 shows a methanol yield of 1475 μmol·g−1, roughly 4.5 times higher than WO3-A2.0 under simulated solar light irradiation. The selectivity of CH3OH on the optimal WO3−x-N2.0 is up to 76%. More importantly, WO3−x-N2.0 exhibits a methanol yield of 396 μmol·g−1 with the selectivity of 82% even under near infrared light irradiation while almost no CH3OH is detected over WO3-A2.0. Based on the results of energy-band structure, photoelectrochemical characterization, PLs and EPR tests, the significantly enhanced photocatalytic performance over WO3−x-N2.0 is ascribed to the synergistic effect caused by the formation of oxygen vacancies, including extending light absorption into NIR region, improving separation of photoinduced electron-hole pairs and boosting production of hydroxyl radicals (key active species that drive CH3OH production). This work will offer a sustainable pathway to broaden the utilization of LC-CMM via efficient coupling of solar energy.