The direct synthesis of dimethyl carbonate (DMC) from carbon dioxide and methanol is an atom economic, green and promising process. The present work focuses on this process using calcined hydrotalcite (CHT) supported on hexagonal mesoporous silica (HMS) as a catalyst and phosphonium based ionic liquid (IL) as a promoter. Phosphonium based ionic liquids are good solvents for carbon dioxide and are better alkali promoters. Different modified Keggin type cesium modified heteropoly acids (HPA) supported on HMS were also used as catalysts, which give good comparison between dual site catalysts with altered acidity or/and basicity. The conversion and selectivity were measured as a function of concentration of reactants, catalyst and temperature. The experimental results were compared with the thermodynamic calculations and simulated results. Kinetic model was developed by proposing a reaction mechanism. Sustainability of the process was justified by using a heterogeneous catalyst and by avoiding the use of harmful organic solvents in the presence of an ionic liquid with supercritical CO2. (C) 2016 Elsevier B.V. All rights reserved.