Optimizing the reaction pathway of methane photo-oxidation over single copper sites

Direct photocatalytic conversion of methane to value-added C₁ oxygenate with O₂ is of great interest but presents a significant challenge in achieving highly selective product formation. Herein, a general strategy for the construction of copper single-atom catalysts with a well-defined coordination microenvironment is developed on the basis of metal-organic framework for selective photo-oxidation of CH₄ to HCHO. We propose the directional activation of O₂ on the mono-copper site breaks the original equilibrium and tilts the balance of radical formation almost completely toward •OOH. The synchronously generated •OOH and •CH₃ radicals rapidly combine to form HCHO while inhibiting competing reactions, thus resulting in ultra-highly selective HCHO production (nearly 100%) with a time yield of 2.75 mmol g_cat^-1 h^-1. This work highlights the potential of rationally designing reaction sites to manipulate reaction pathways and achieve selective CH₄ photo-oxidation, and could guide the further design of high-performance single-atom catalysts to meet future demand.