Computational study of the conversion of methane and carbon dioxide to acetic acid over NU-1000 metal–organic framework-supported single-atom metal catalysts

Abstract

The conversion of methane (CH4) and carbon dioxide (CO2) to more valuable chemicals is attracting attention from an industrial and environmental perspective; however, this process is a great challenge in catalysis, because of the high stabilities of CH4 and CO2. Herein, we investigate the CH4 and CO2 conversion to acetic acid over NU-1000 metal–organic framework (MOF)-supported single-atom catalysts (SACs) (M-NU-1000, M = Mn, Fe, Co, Ni, and Cu) using density functional calculations. The reaction proceeds in three steps: first, a CH4 C–H bond dissociates to form a methyl intermediate. Then, an acetate intermediate is formed via C–C bond coupling between the methyl carbon atom and CO2. Finally, the acetate abstracts a proton to form the acetic acid product. We discover that Cu-NU-1000 exhibits the highest catalytic activity as compared to the other catalysts, based on its overall reaction barrier and rate constants. We also disclose two suitable descriptors to approximately predict the overall activation barrier of the reaction. One is the complexation energies difference between CO2 adsorbed on a methyl intermediate and CH4 adsorbed on the SACs used in this study. Another plausible descriptor is the difference between complexation energies of acetate intermediate and the CH4 adsorption. The supported NU-1000 MOFs are also found to accelerate the stability of all species formed along the reaction coordinates, especially during the transition states.