Efficient and Selective Thermal-Assisted Photocatalytic Methane-to-Formaldehyde Conversion on Defect-Engineered Ag/WO ₃

Direct photocatalytic conversion of methane to formaldehyde (HCHO) provides a sustainable route for methane valorization. However, the exceptional inertness of the C–H bond in methane and the propensity of oxygenated products toward overoxidation have hindered the simultaneous achievement of high selectivity and appreciable productivity. Here, we report a highly efficient photocatalyst comprising metallic Ag nanoparticles anchored on oxygen-vacancy-rich WO3, which delivers a state-of-the-art HCHO yield of 28.5 mmol g–1 for 4 h with an outstanding selectivity of 96.6% under mild photothermal conditions (150 °C). Operando spectroscopic characterizations combined with theoretical calculations reveal that the interfacial synergy between Ag species and oxygen vacancies markedly enhances charge separation and enables the selective activation of CH4 and O2 into •CH3 and •OOH radicals, respectively. Moreover, moderate thermal activation accelerates the reaction kinetics while facilitating rapid HCHO desorption from the catalyst surface, thereby effectively suppressing overoxidation to CO2. This work establishes an effective strategy for selective methane valorization through the rational coupling of interfacial defect engineering and photothermal synergy, providing insights for the design of advanced photocatalytic C1 conversion systems.