Photocatalytic Oxidative Coupling of Methane to Ethane Using CO2 as a Soft Oxidant over the Au/TiO2−Vo Nanosheets

Abstract Photocatalytic oxidative coupling of methane (OCM) offers an appealing route for converting greenhouse gas into valuable C 2 hydrocarbons. However, O 2, as the most commonly used oxidant, tends to result in inevitable overoxidation and waste of methane feedstock. Herein, we first report a photocatalytic OCM using CO 2 as a soft oxidant for C 2 H 6 production under mild conditions, where an efficient photocatalyst with unique interface sites is designed and constructed to facilitate CO 2 adsorption and activation, while concurrently boosting CH 4 dissociation. As a prototype, the Au quantum dots anchored on oxygen‐deficient TiO 2 nanosheets are fabricated, where the Au−V o −Ti interface sites for CO 2 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−V o −Ti interface sites exhibit the lower CO 2 adsorption energy and decrease the energy barrier of the *CO 2 hydrogenation step from 1.05 to 0.77 eV via Au−C and Ti−O dual‐site bonding. The adsorbed CO 2 on the photocatalyst reduces the energy barrier of *CH 4 dissociation to *CH 3 from 2.13 to 1.59 eV, contributing to CH 4 oxidation. Additionally, in situ Fourier‐transform infrared spectroscopy unveils the Au site facilitates ethane production by engaging in *CH 3 −Au interaction and accelerating CH 3 −CH 3 coupling. Thus, the photocatalyst demonstrates a high C 2 H 6 evolution rate of 2.60 mmol g −1 h −1 for OCM using CO 2 as the soft oxidant, surpassing most of previously reported photocatalysts regardless of OCM and nonoxidative coupling of methane. This work highlights the importance of soft oxidants for improving oxidation reaction efficiency and provides atomic scale insight into the design of photocatalysts for CH 4 conversion.