Facet‐Dependent Oxygen‐Vacancy Electronic Delocalization Governs Photocatalytic Oxidative Coupling of Methane Over Au/CeO 2

ABSTRACT Metal/metal‐oxide catalysts are widely studied for photocatalytic oxidative coupling of methane (OCM), and oxygen vacancies are often invoked to enhance catalytic performance. However, oxygen vacancies are usually discussed separately from metal sites, and their cooperative effects, especially on C 2+ selectivity, remain poorly understood. Here, we reveal that the delocalized electronic character of oxygen vacancy governs both activity and selectivity in Au/CeO 2 , while elevated temperature further enhances the delocalization. By facet engineering CeO 2 , we create oxygen vacancies with tunable properties and find that Au/CeO 2 ‐R with exposed {110} facets achieves a CH 4 conversion rate of 14 mmol g −1 h −1 and a C 2+ selectivity of 86% at 200°C, whereas the other facet‐defined Au/CeO 2 catalysts produce no detectable C 2+ products. This performance places Au/CeO 2 ‐R among the best‐reported photocatalytic OCM catalysts. Mechanistic studies reveal that oxygen vacancies on CeO 2 {110} exhibit higher electronic delocalization, which promotes O 2 activation and induces stronger support‐Au charge redistribution, strengthening the Au─C interaction and favoring methyl coupling. These findings identify electronic delocalization as a key parameter for designing defect‐mediated photocatalysts for selective OCM.