Dibutyltin oxide or dibutyltin dimethoxide was first used as a remarkable selective catalyst for the synthesis of propylene carbonate from propylene glycol and carbon dioxide. The effects of the reaction parameters, such as reaction time, temperature and CO2 pressure on the amount of propylene carbonate were also experimentally studied. Under the optimized conditions, the amount of propylene carbonate was nearly proportional to PG concentration. The use of N, N-dimethylformamide as a co-solvent in this study significantly enhanced the catalytic activity, and the ketals as dehydrating agents greatly improved the yield of PC, which can be limited by the equilibrium. A postulated mechanism for the dibutyltin oxide-catalyzed carboxylation of propylene glycol was also discussed.

Lanthanide oxychloride, especially SmOCl, is an efficient solid catalyst for propylene carbonate synthesis from supercritical CO2 and propylene oxide. The process requires no additional organic solvents and the product is automatically separated out from the CO2 phase.

Tetraalkylammonium salts of transition-metal-substituted polyoxometalates, such as [(n-C7H15)4N]6[α-SiW11O39Co] and [(n-C7H15)4N]6[α-SiW11O39Mn], efficiently catalyze cyclic carbonate synthesis from carbon dioxide and epoxide. The catalytic activity is significantly influenced by the type of transition metal and the countercation (Co2+≈Mn2+>Ni2+>Fe3+»Cu2+; (n-C7H15) 4N+>(n-C4H9)4N+»K+). Co- or Mn-substituted catalysts required neither additional organic solvents nor additives. Thus, polyoxometalates are promising as nonhalogen anionic components of catalysts for cyclic carbonate synthesis.

A PEG-supported quaternary ammonium salt is proved to be an efficient and recyclable homogeneous catalyst for solvent-free synthesis of cyclic carbonates from carbon dioxide and epoxides under supercritical conditions. Supporting Bu4NBr onsoluble polymer PEG6000 enhances the catalytic activity. The workup procedure is straightforward, and the catalyst can be reused over five times with no appreciable loss of catalytic activity and selectivity.

Insoluble ion exchange resins, one type of polystyryl supported catalysts containing an ammonium salt or amino group, and the polar macroporous adsorption resin, are efficient and reusable heterogeneous basic catalysts for the synthesis of propylene carbonate from propylene oxide and CO2 under supercritical CO2 conditions (373K, 8MPa), which requires no additional organic solvents either for the reaction or for the separation of product. Various parameters affecting the reaction were examined. A quantitative yield (>99%) together with excellent selectivity (>99%) was obtained. The purity of product separated directly by filtration from the reaction mixture, reached more than 99.3% without further purification processes. The catalyst can be easily recovered and reused without significant loss of its catalytic activity. The process represents a simple, ecologically safer, cost-effective route to cyclic carbonates with high product quality, as well as easy product recovery and catalyst recycling.