Near-100% Selective Photocatalytic Methane-to-Methanol Conversion Enabled by Synergistic Chlorine Radicals and Oxygen Vacancies.

The selective photocatalytic conversion of methane to a single product is a grand challenge, primarily due to uncontrollable over-oxidation and inefficient reduction. Herein, we pioneer a radical/active-site synergistic strategy to steer the reaction pathway exclusively toward methanol. This is realized by a dual-functional Cl─TiO2-OV catalyst that integrates chlorine modification and oxygen vacancy (OV) engineering. Crucially, surface chlorine redirects the oxidation route: instead of generating non-selective •OH radicals from H2O, photogenerated holes preferentially drive a Cl-/Cl• cycle. The resulting Cl• radicals activate the C─H bond of CH4 to form •CH3, which combines with O2 to yield the CH3OOH intermediate. Simultaneously, the engineered OV sites act as electron-rich centers that efficiently reduce CH3OOH to CH3OH. This decoupling of selective oxidation (via Cl•) and efficient reduction (via OVs) suppresses all side-reactions, delivering methanol with nearly 100% selectivity and a yield of 1242 µmol g-1. In contrast, TiO2-OV suffers from •OH-mediated sequential oxidation to HCHO/CO2, and Cl─TiO2 lacks sufficient reduction power, resulting in a CH3OOH/CH3OH mixture. This work not only offers an effective approach for highly selective photocatalytic methane conversion but also deepens mechanistic insight into radical/active-site cooperativity in synergistic catalysis.