Oxidative‐Branch Engineering for Radical Regulation in Methane‐to‐Methanol Photocatalysis

Selective methane‐to‐methanol photocatalysis requires efficient methane activation and control over the radical environment that determines whether methanol is preserved or further oxidized. Radical generation is therefore double‐edged: an underdeveloped radical environment limits C–H activation and methanol‐forming oxygenation, whereas an excessive oxidative environment promotes secondary oxidation. Here, the radical environment is regulated by engineering the oxidative branch of an In 2 O 3 /ZnO S‐scheme heterojunction. Under ambient‐pressure gas–solid flow conditions with O 2 and H 2 O as co‐reactants, the optimized catalyst delivers methanol at 638.2 µmol g −1 h −1 with 93.8% selectivity. The volcano‐shaped dependence of methanol productivity on ZnO loading shows that methanol accumulation is governed by competition between partial and deep oxidation rather than oxidative strength alone. Spectroscopic analyses support an S‐scheme charge‐transfer pathway that preserves oxidative holes on ZnO and reductive electrons on In 2 O 3 , coupling methane activation, water oxidation and O 2 reduction within a branch‐specific redox network. Increasing ZnO loading strengthens the methyl‐, superoxide‐ and hydroxyl‐radical probe responses, whereas methanol selectivity peaks at an intermediate loading. At higher ZnO loading, deep‐oxidation signatures emerge without further enhancement of methanol‐related surface chemistry, whereas the optimized heterojunction maintains a formation‐dominant surface pathway. These findings identify a kinetic balance in the radical environment, rather than radical maximization, as the selectivity principle for methane‐to‐methanol photocatalysis.