Catalytic oxidation of CH₄ into CH₃OH using C₂₄N₂₄-supported single-atom catalyst

Methanol is a promising source that can replace non-renewable petroleum energy. Therefore, it is of great importance to oxidize the methane into methanol because methane is not easy to transport although its huge reserves. The stability between TM (Ti, V) atoms and C₂₄N₂₄ is firstly studied through DFT calculations. The results show that the binding energy between TM and C₂₄N₂₄(Ti@C₂₄N₂₄ =  - 9.0 eV, V@C₂₄N₂₄ =  - 8.0 eV) is more negative than its cohesive energy (Ti =  - 5.6 eV, V =  - 5.6 eV), indicating TM@C₂₄N₂₄ possess good stability. On this basis, the oxidation process of methane to methanol is further studied on the TM@C₂₄N₂₄ single-atom catalysis using N₂O as the oxidant. The results show that N₂O is firstly adsorbed on TM@C₂₄N₂₄, and then directly decomposed into N₂ and O_ads. N₂ is released and only O_ads is adsorbed on C₂₄N₂₄ as active oxygen for the following catalytic methane oxidation to methanol process. The process includes two steps: (1) CH₄ + O_ads → CH₃* + OH*, the reaction barriers in this process are 1.2 eV (Ti) and 1.5 eV (V); (2) CH₃* + OH* → CH₃OH, the reaction barriers are 1.8 eV (Ti) and 1.8 eV (V) in this step. Finally, the obtained CH₃OH molecule will leave the surface of TM@C₂₄N₂₄ single-atom catalyst and the energy required for this step is 1.4 eV (Ti) and 1.0 eV (V), respectively. These findings provide theoretical guidance for the catalytic oxidation of CH₄ to CH₃OH using TM (Ti,V)@C₂₄N₂₄ single-atom catalysts.