A selective Au-ZnO/TiO2 hybrid photocatalyst for oxidative coupling of methane to ethane with dioxygen

Direct oxidation of methane to valuable chemicals is a great challenge as catalysts with both high activity and selectivity for the activation of inert C–H bonds are required. Here, we report the highly efficient and selective photo-oxidation of methane to ethane with dioxygen in a flow reactor using a Au nanoparticle (NP) loaded ZnO/TiO2 hybrid. An ethane production rate of over 5,000 μmol g−1 h−1 with 90% selectivity is achieved, which is more than one order of magnitude higher than the state-of-the-art photocatalytic systems. Detailed characterizations and theoretical studies show that the formation of heterojunctions between ZnO and TiO2 leads to enhanced photocatalytic activity, while maintaining high selectivity owing to the weak overoxidation ability of the main component ZnO. Moreover, the Au cocatalyst enables the facile desorption of methyl (CH3) species as •CH3 radicals in the gas phase, thereby facilitating C2H6 formation and inhibiting overoxidation of CH4 to CO2. Photocatalytic oxidation of methane through oxidative coupling presents a route to higher hydrocarbons but has suffered from low activity and uncontrolled product selectivity. Now, Au nanoparticles loaded onto a ZnO/TiO2 heterostructure are shown to deliver high rate production of ethane.