Selective Photocatalytic Oxidative Coupling of Methane via Regulating Methyl Intermediates over Metal/ZnO Nanoparticles

Abstract

Methane conversion to higher hydrocarbons requires harsh reaction conditions due to high energy barriers associated with C−H bond activation. Herein, we report a systematic investigation of photocatalytic oxidative coupling of methane (OCM) over transition-metal-loaded ZnO photocatalysts. A 1 wt % Au/ZnO delivered a remarkable C₂-C₄ hydrocarbon production rate of 683 μmol g⁻¹ h⁻¹ (83 % C₂-C₄ selectivity) under light irradiation with excellent photostability over two days. The metal type and its interaction with ZnO strongly influence the selectivity toward C−C coupling products. Photogenerated Zn⁺-O⁻ sites enable CH₄ activation to methyl intermediates (*CH₃) migrating onto adjacent metal nanoparticles. The nature of the *CH₃-metal interaction controls the OCM products. In the case of Au, strong d-σ orbital hybridization reduces metal-C−H bond angles and steric hindrance, thereby enabling efficient methyl coupling. Findings indicate the d-σ center may be a suitable descriptor for predicting product selectivity during OCM over metal/ZnO photocatalysts.