Mechanistic Insights into Direct Methane Oxidation to Methanol on Single-Atom Transition-Metal-Modified Graphyne

Methane is the major component in natural gas and flares wastefully at remote sites since the collection and use are not economical. The direct conversion of methane into liquid fuels such as methanol has been identified as a fruitful solution to this issue. Herein, density functional theory calculations and microkinetic studies were employed on 3d late-transition-metal atom (Fe, Co, Ni, Cu)-loaded graphyne as catalysts for methane-to-methanol conversion. Single metal atoms showed decent stability at pores of graphyne. The oxidant used for this work was abundant O2 instead of high-cost H2O2 or N2O. This systematic study revealed that both iron and cobalt single atoms dispersed at adjoining pores of graphyne are capable of forming catalytically active metal–oxygen (M–O) moieties upon dissociative adsorption of O2. Further, the Co–O moiety loaded on graphyne demonstrated reasonable catalytic activity for methane-to-methanol conversion with sufficient selectivity. Interestingly, dispersed single metal atoms on graphyne support were able to mimic the enzymatic formation of catalytically active M–O moieties. Moreover, it is further noticed that methane activation and methanol production kinetics are strongly correlated with the strength of the metal–oxygen bond.