Photocatalytic Oxidative Coupling of Methane to Ethane Using CO2 as a Soft Oxidant Over the Au/TiO2-Vo Nanosheets.

Herein, we first report a photocatalytic OCM using CO2 as a soft oxidant for C2H6 production under mild conditions, where an efficient photocatalyst with unique interface sites is constructed to facilitate CO2 adsorption and activation, while concurrently boosting CH4 dissociation. As a prototype, the Au quantum dots anchored on oxygen-deficient TiO2 nanosheets are fabricated, where the Au-Vo-Ti interface sites for CO2 adsorption and activation are collectively disclosed by in situ Kelvin probe force microscopy, quasi in situ X-ray photoelectron spectroscopy and theoretical calculations. Compared with single metal site, the Au-Vo-Ti interface sites exhibit the lower CO2 adsorption energy and decrease the energy barrier of the *CO2 hydrogenation step from 1.05 to 0.77 eV via Au-C and Ti-O dual-site bonding. The adsorbed CO2 reduces the energy barrier of *CH4 dissociation to *CH3 from 2.13 to 1.59 eV, contributing to CH4 oxidation. Additionally, in situ Fourier-transform infrared spectroscopy unveils the Au site facilitates ethane production by engaging in *CH3-Au interaction and accelerating CH3-CH3 coupling. Thus, the photocatalyst demonstrates a high C2H6 evolution rate of 2.60 mmol g-1 h-1 for OCM using CO2 as the soft oxidant, surpassing most of previously reported photocatalysts regardless of OCM and nonoxidative coupling of methane.