The role of coordination-unsaturated Cu₁-O₃ species in the single-atom catalyst Cu/In₂O₃ for the preparation of acetic acid from methane and carbon dioxide

The co-conversion of CH₄ and CO₂ has emerged as a challenging issue in C1 chemistry. Converting these gases into a high-value product like acetic acid is an attractive solution. In this study, we employed density-functional theory calculations to design dual-active single-atom catalysts M/In₂O₃ (M=Co, Ni, Cu, Zn, Rh, Pd, Ag, Cd), which incorporated oxygen vacancies. These catalysts were created by introducing metal M into the surface of In₂O₃ (111) through doping. Cu/In₂O₃, Zn/In₂O₃, Ag/In₂O₃, and Cd/In₂O₃ were selected based on the stability of forming single-atom catalysts. Our findings indicated that the formation of the M/In₂O₃ surface activates the In surface activity and significantly lowers the activation energy for methane dehydrogenation. Among them, the Cu₁-O₃ species on the Cu/In₂O₃ surface demonstrates a lower activation energy for methane dehydrogenation and C-C coupling reactions. The "H-O-C-O" hydrogenation of CH₃COO* species bonded with the "n"-type structure is more realistic. Microkinetic analysis indicated that the average turnover frequency for the forming of acetic acid on the Cu/In₂O₃ surface is three orders of magnitude greater than that of methyl formate. This research provides theoretical support for the development of copper single-atom catalysts for the efficient conversion of CO₂ and CH₄ into acetic acid.