Synergistic Au and ZnO Sites Decorated on TiO ₂ Steering Methane Photocatalytic Oxidative Coupling to Ethane

The selective photocatalytic oxidative coupling of methane (OCM) offers a mild route to ethane synthesis but usually suffers from low yields and CH4 overoxidation. Here, Au and ZnO nanoparticles decorated on TiO2 were designed as active and stable catalysts to realize efficient C–H dissociation and selective C–C coupling. The optimal Au–ZnO/TiO2 (metal loadings: 1.5% Au and 1.0% ZnO) catalyst achieved a high C2H6 production rate of 17.02 mmol g–1 h–1 at a superior selectivity of 90.1% under xenon lamp irradiation and further maintained a stable activity for 120 h. This result significantly outperformed the most active Au- and Ag-supported photocatalysts reported to date in the literature. Physical and photoelectronic characterizations, in situ spectroscopy, and DFT calculations revealed Au and ZnO as the essential active sites for the OCM-to-C2H6 reaction, and their synergism is responsible for the outstanding performance. Small Au and ZnO nanoparticles (ca. 2–3 nm) decorated on TiO2 can enhance light harvesting, accelerate charge separation, and prolong carrier lifetime. CH4 and O2 were found to adsorb and activate on Au and ZnO sites to forming •CH3 and •O2–/•O– reactive intermediates, sustaining the photocatalytic OCM. ZnO was shown to obviously reduce the energy barrier for C–H cleavage and promote O2 dissociation at oxygen vacancy, while electron-rich Au was disclosed to facilitate •CH3 migration and C–C coupling via lower barriers. Therefore, the synergistic catalysis between Au and ZnO primely overcomes the activity-selectivity trade-off and enables high C2H6 production by suppressing CH4 overoxidation to CO2.