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In this study, a density functional theory method is employed to investigate the reaction mechanisms of dimethyl carbonate (DMC) formation, through oxidative carbonylation of methanol, on four types of Y zeolites doped with Cu⁺, Cu²⁺, Cu₂O and CuO, respectively. A common chemical route is found for these zeolites and identified as, first, the adsorbed CH₃OH is oxidized to CH₃O species; subsequently, CO inserts into CH₃O to CH₃OCO, which reacts with CH₃O to form DMC rapidly; and finally, the adsorbed DMC is released into the gas phase. The rate-limiting step on Cu²⁺Y zeolite is identified as oxidation of CH₃OH to CH₃O with activation barrier of 66.73 kJ·mol⁻¹. While for Cu⁺Y, Cu₂O-Y and CuO-Y zeolites, the rate-limiting step is insertion of CO into CH₃O, and the corresponding activation barriers are 63.73, 60.01 and 104.64 kJ·mol⁻¹, respectively. For Cu⁺Y, Cu²⁺Y and Cu₂O-Y zeolites, adsorbed CH₃OH is oxidized to CH₃O with the presence of oxygen, whereas oxidation of CH₃OH on CuO-Y is caused by the lattice oxygen of CuO. The order of catalytic activities of these four types of zeolites with different Cu states follows Cu⁺Y ≈ Cu₂O-Y > Cu²⁺Y > CuO-Y zeolite. Therefore, CuY catalysts with Cu⁺ and Cu₂O as dominated Cu species are beneficial to the formation of DMC.