Graphene-Supported Single-Atom Ni as High-Performance Catalyst for Direct Methane-to-Methanol Conversion

Inspired by the excellent performance of NiO⁺ in converting CH₄ to CH₃OH in the gas phase and the efficiency of single-atom catalysts, we constructed a Ni-O active site on single-vacant (SV) graphene by using O₃/N₂O as the oxidant. Quantum chemistry calculations predict Ni/SV-graphene to be a potential catalyst for CH₄-to-CH₃OH conversion, outperforming Pd or Pt/SV-graphene in both the activity and selectivity. The radical pathway is favored, and the C-H bond activation is the rate-determining step, during which an electron is transferred from CH₄ to the O-atom of OM/SV-graphene and pushes an electron from σ_M-O orbital to σ_M-O^*. The ONi/SV-graphene has smaller σ_M-O^* to σ_M-O energy gap than its Pd/Pt counterparts, thus more readily transferring the electron to activate the C-H bond, making it the best catalyst. In addition, Ni/SV-graphene is capable of recycling and avoiding overoxidizing of methanol. This study provides theoretical insights into developing efficient noble-metal-free catalysts for direct CH₄-to-CH₃OH conversion.