Enhanced Photocatalytic Oxidative Coupling of Methane over Metal-Loaded TiO2 Nanowires

The photocatalytic oxidative coupling of methane (OCM) on metal-loaded one-dimensional TiO2 nanowires (TiO2 NWs) was performed. With metal loading, the electric and optical properties of TiO2 NWs were adjusted, contributing to the improvement of the activity and selectivity of the OCM reaction. In the photocatalytic OCM reaction, the 1.0 Au/TiO2 NW catalyst exhibits an outstanding C2H6 production rate (4901 μmol g−1 h−1) and selectivity (70%), alongside the minor production of C3H8 and C2H4, achieving a total C2–C3 hydrocarbon selectivity of 75%. In contrast, catalysts loaded with Ag, Pd, and Pt show significantly lower activity, with Pt/TiO2 NWs producing only CO2, indicating a propensity for the deep oxidation of methane. The O2-TPD analyses reveal that Au facilitates mild O2 adsorption and activation, whereas Pt triggers excessive oxidation. Spectroscopic and kinetic studies demonstrate that Au loading not only enhances the separation efficiency of photogenerated electron–hole pairs, but also promotes the generation of active oxygen species in moderate amounts, which facilitates the formation of methyl radicals and their coupling into C2H6 while suppressing over-oxidation to CO2. This work provides novel insights and design strategies for developing efficient photocatalysts.