In Situ 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 in situ 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 in situ/operando techniques for establishing the structure–activity relation of catalysts “at work”.