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 Oads. N2 is released and only Oads is adsorbed on C24N24 as active oxygen for the following catalytic methane oxidation to methanol process. The process includes two steps: (1) CH4 + Oads → 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.