Direct synthesis of diethyl carbonate (DEC) from propylene oxide, CO2 and ethanol via coupling reaction over a heterogeneous catalyst was demonstrated. In this work, a cross linked poly(ionic liquid) containing poly(1-vinyl-3-ethylimidazolium bromide)(PVEImBr) moiety was prepared via a free radical polymerization. Meanwhile, the MgO nanoplatelet with abundant basic sites was prepared, which was combined with PVEImBr to form a composite catalyst of PVEImBr/MgO center dot N-2 physisorption, TG, XRD, SEM, CO2-TPD and FT-IR were conducted to thoroughly characterize the structure and texture of the catalysts. The as prepared heterogeneous catalyst, which simultaneously possessed the dual function of nucleophilicity and basicity, was used in the coupling reaction of propylene oxide, CO2 and ethanol to synthesize diethyl carbonate and propylene glycol. The composite catalyst could promote the reaction with high efficiency, and a good catalytic performance of 54.4% diethyl carbonate yield and 59.8% propylene glycol yield could be achieved. The H-1 NMR and DFT calculation disclosed that greatly faster reaction rate was ascribed to the synergistic effect between the Br circle dot anion of PVEImBr and hydroxyl group of ethanol. Accordingly, a mechanism of the sequential reaction consisting of cycloaddition and transesterification steps was proposed. (C) 2016 Elsevier B.V. All rights reserved.