Enzyme-Mimicking Copper Single-Atom Catalyst for Selective Oxidation of Methane to Liquid Oxygenates.

Direct methane conversion (DMC) to oxygenates with high reactivity and selectivity represents one of the greatest challenges in catalysis. Herein, we report an enzyme-mimicking Cu single-atom catalyst for efficient DMC using HO and O as the oxidant. Upon oxidation with HO, Cu single atoms are stabilized in the form of N-Cu-O at the zigzag edge of carbon nitride, endowing highly covalent Cu-O pair for homolytic C-H cleavage of methane (diameter of 3.78 Å) with a low barrier of 0.58 eV. Importantly, the formed methyl radicals could be captured by O and generate CHOOH (diameter >4.2 Å) as the primary product, whose back diffusion and overoxidation over Cu are retarded via the steric hindrance of the zigzag edge that holds a "V-type" configuration with an entrance width of 3.87 Å. Such synergy between active centers and the specific steric hindrance of the surrounding geometric structure, analogous to the gating mechanism of methane monooxygenase, gives a high turnover frequency of 405.3 ± 8.2 h with ∼100% selectivity at 50 °C.