The direct synthesis of dimethyl carbonate from carbon dioxide and methanol is an atom economic, green and promising process. The present work focuses on the same using calcined hydrotalcite supported on hexagonal mesoporous silica as a catalyst and phosphonium based ionic liquid as promoter. Ionic liquids are good solvents for many substances and have shown good results as promoters for the catalyst. The phosphonium based ionic liquids are good alkali promoters. Different modified Keggin type heteropoly acids supported on hexagonal mesoporous silica were also compared, which gives a good comparison between acid and base catalysts. The conversion, selectivity and yields were measured as a function of the amount of reactants, reaction time, temperature, pressure and amount of a catalyst. The experimental results were compared with the thermodynamic studies. Finally the kinetic model was developed by proposing a plausible reaction mechanism. Sustainability of the process was justified by using a supported hydrotalcite catalyst and by avoiding the use of harmful organic solvents in the presence of an ionic liquid with supercritical CO2.
Key words: Carbon dioxide, Dimethyl carbonate, Ionic liquids, Supercritical CO2, Calcined Hydrotalcite, Heteropoly acids.