Roles of titania and plasmonic gold nanoparticles of different sizes in photocatalytic methane coupling at room temperature

Abstract

Methane, one of the most abundant molecules on Earth and a major greenhouse gas, comes from renewable and fossil resources. The utilization of methane as a starting material for synthesis of chemicals is attractive but encounters numerous challenges due to high thermodynamic stability and extreme inertness of methane. Most of methane reactions occur at high temperatures and coincide with major emissions of CO2. Semiconductor photocatalysis offers an efficient alternative for methane conversion at room temperature.In this paper, we studied the plasmonic gold nanoparticles (NPs) with size from 6 nm to 60 nm supported on titania semiconductor in methane nonoxidative and oxidative couplings and elucidated their roles in the reactions. Strikingly, an efficient oxidative coupling with ethane production of 819 μmol/g/h and a coupling selectivity up to 86% was achieved in a flow reactor under optimized conditions. The reaction proceeded through methane activation over oxygen vacancies on Ultraviolet-excited titania. Gold NPs played important roles in charge separation and provided sites for soft oxygen activation. The size of gold NPs was found to be not noticeably affecting methane coupling.