Direct Photocatalytic Oxidation of Methane to Formic Acid with High Selectivity via a Concerted Proton–Electron Transfer Process

Light-driven direct conversion of methane to formic acid is a promising approach to convert methane to value-added chemicals and promote sustainability. However, this process remains challenging due to the complex requirements for multiple protons and electrons. Herein, we report the design of WO₃-based photocatalysts modified with Pt active sites to address this challenge. We demonstrate that modulating the dimensional effect of Pt on the WO₃ support is key to enhancing the catalytic performance of selective CH₄-to-HCOOH conversion. The Pt nanoparticles on WO₃ exhibit superior conversion rate, selectivity and durability in the production of HCOOH compared to the Pt-free sample and WO₃ decorated with Pt single atoms. The optimal PtNPs-WO₃ catalyst achieves a HCOOH conversion rate of 17.7 mmol g⁻¹, with 84% selectivity and stability maintained for up to 48 h. Mechanistic studies show that the protonation of O₂ to hydroxyl radicals is the limiting step for HCOOH yield. Pt nanoparticles can facilitate electron transfer and promote O₂ dissociation, generating hydroxyl radicals via a proton-coupled electron transfer process. This process provides sufficient protons to lower the formation barrier for •OH radicals, thereby promoting the activation of CH₄. In addition, Pt nanoparticles regulate the adsorption of oxygenated hydrocarbon intermediates, increasing the selectivity of the reaction. This work advances our understanding of catalyst design for methane conversion and the effective regulation of complex reaction pathways.