H 2O 2 is widely used as an oxidant for photocatalytic methane conversion to value-added chemicals over oxide-based photocatalysts under mild conditions, but suffers from low utilization efficiencies. Herein, we report that O 2 is an efficient molecular additive to enhance the utilization efficiency of H 2O 2 by suppressing H 2O 2 adsorption on oxides and consequent photogenerated holes-mediated H 2O 2 dissociation into O 2. In photocatalytic methane conversion over an anatase TiO 2 nanocrystals predominantly enclosed by the {001} facets (denoted as TiO 2{001})-C 3N 4 composite photocatalyst at room temperature and ambient pressure, O 2 additive significantly enhances the utilization efficiency of H 2O 2 up to 93.3%, giving formic acid and liquid-phase oxygenates selectivities respectively of 69.8% and 97% and a formic acid yield of 486 μmol HCOOH·g catalyst −1·h −1. Efficient charge separation within TiO 2{001}-C 3N 4 heterojunctions, photogenerated holes-mediated activation of CH 4 into ·CH 3 radicals on TiO 2{001} and photogenerated electrons-mediated activation of H 2O 2 into ·OOH radicals on C 3N 4, and preferential dissociative adsorption of methanol on TiO 2{001} are responsible for the active and selective photocatalytic conversion of methane to formic acid over TiO 2{001}-C 3N 4 composite photocatalyst.
The oxidation of methane to formic acid or related oxygenates relies on efficient reaction with H 2O 2. Here, the authors report a TiO 2-based catalyst to selectively form formic acid by using molecular O 2 additives to avoid unwanted side reactions.