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.