The mechanism for dimethyl carbonate (DMC) synthesis by oxidation carbonylation of methanol on a single-atom Cu-1/graphene catalyst was investigated by density-functional theory calculations. Carbon vacancies in graphene can significantly enhance the interaction between Cu atoms and graphene supports, and provide an increased transfer of electrons from Cu atoms to the graphene sheet. Compared with Cu-doped divacancy graphene (Cu/DG), Cu-doped monovacancy graphene (Cu/MG) provides a stronger interaction between adsorbents and the catalyst surface. Among the reaction processes over Cu-1/graphene catalysts, CO insertion into methoxide was more favorable than dimethoxide. The ratelimiting step on the Cu/DG surface is the carbomethoxide reaction with methoxide, which is exothermic by 164.6 kJ mol(-1) and has an activation barrier of 190.9 kJ mol(-1) energy. Compared with that on the Cu crystal surface, Cu-4 and Cu3Rh clusters, and the Cu2O(111) surface, the rate-determining step for DMC formation on Cu/MG, which is CO insertion into methoxide, needs to overcome the lowest barrier of 73.5 kJ mol(-1) and is exothermic by 44.6 kJ mol-1. Therefore, Cu/MG was beneficial to the formation of DMC as a single-atom catalyst. (C) 2017 Elsevier B.V. All rights reserved.