<i>In Situ</i> Generated Ti³⁺ over Ag/TiO₂ Enables Highly Efficient Photocatalytic Oxidative Coupling of Methane in Flow Reactors

Photocatalytic oxidative coupling of methane (OCM) is a promising sustainable technology for chemical and fuel synthesis, but current photocatalysts suffer from limited activity and selectivity. Here, we report a highly active Ag/TiO₂ catalyst for OCM in a flow reactor, achieving a C₂ hydrocarbon production rate of 1.9 mmol g^-1 h^-1 and selectivity of up to 92% with enhanced stability exceeding 150 h. This performance surpasses that of most reported semiconductor-based photocatalysts. The enhanced performance is attributed to a synergistic effect between <i>in situ</i> photogenerated Ti³⁺ and Ag on TiO₂, where Ti³⁺ acts as a hole trap promoting hole transfer and C-H activation, and Ag serves as an electron acceptor and catalytic center to accelerate electron transfer and C-C coupling. These findings not only provide valuable mechanistic insights into photocatalytic OCM but also demonstrate the utility of <i>in situ</i>/operando techniques for establishing the structure-activity relation of catalysts "at work".