Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single Atom Sites on Carbon Nitride for Selective Photooxidation of Methane into Methanol

Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer-Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIIIO) sites and selective CH bond cleavage to generate center dot CH3 radicals on Ni centers, which can combine with center dot OH radicals to generate CH3OH. Performing selective photooxidation of methane into methanol under visible light using an inexpensive and robust Ni single atom catalysts. The catalyst synthesis involves two steps: i) nickel complexation with melem units; ii) thermal condensation. Melem units prevent the probability of metal coarsening during thermal treatment generating unsymmetrical tetra-coordinated Ni-N4 sites embedded in the heptazine cavity.image