Computational Study of Methane Direct Oxidation to Methanol on g-C 3 N 4 -Based Single Metal Atom Catalysts

The direct conversion of methane to methanol is a promising strategy for the utilization of abundant natural resources with significant economic benefits. However, this process still faces substantial challenges in both activity and selectivity. In this work, based on density functional theory calculations, the potential of single-atom catalysts TM@g-C 3 N 4 (TM = Cr, Fe, Co, Ni, Cu) for the oxidation of methane to methanol with N 2 O as the oxidant was systematically investigated. The results show that, except for Fe, TM@g-C 3 N 4 can be easily oxidized to the TM-O@g-C 3 N 4 species, which effectively suppresses side reactions and exhibits excellent selectivity toward methane-to-methanol conversion via a radical mechanism. Notably, the first C–H bond activation of CH 4 is identified as the rate-determining step for all TM-O@g-C 3 N 4 species, and the reaction activity increases in the order of the periodic table. Electronic structure analysis reveals that the oxygen atom in Cu-O@g-C 3 N 4 carries the highest negative charge, leading to the strongest C–H···O interaction and the lowest energy barrier for C–H bond cleavage. The energy barrier for C–H activation (0.44 eV) is similar to that for the formation of Cu-O@g-C 3 N 4 (0.47 eV). Additionally, the excellent stability of Cu@g-C 3 N 4 and Cu-O@g-C 3 N 4 guarantees superior catalytic performance under ambient conditions, confirming that Cu@g-C 3 N 4 is an ideal catalyst for methane-to-methanol conversion. Our findings open a new avenue for the rational design of single-atom catalysts for methane oxidation to methanol.