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.

Supercritical carbon dioxide is efficiently converted to dimethyl carbonate (DMC) via the reaction with methanol in the presence of a catalytic amount of dialkyltin oxide or its derivatives. The removal of water is the key to accomplishing the high conversion by shifting the equilibrium to dimethyl carbonate. Dehydration is successfully carried out by circulating the reaction mixture through a dehydrating tube packed with molecular sieve 3A. Under the effective dehydration conditions, the DMC yield is almost linearly dependent on the reaction time, catalyst amount, methanol concentration, and CO2 pressure.

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.

A homogenous binary catalyst system, n-Bu4NBr/n-Bu3N, was found to be active for the synthesis of dimethyl carbonate from styrene oxide (SO), methanol, and supercritical CO2. Under the optimized conditions, the dimethyl carbonate yield could reach 84% at SO conversion of 98%. Several parameters were studied, i.e. catalyst precursors, reaction time and temperature, methanol/epoxide feed ratio in moles, and CO2 pressure. The best compromise for the one-pot synthesis was achieved with an equimolar amount of n-Bu4NBr/n-Bu3N. A possible mechanism for the present n-Bu4NBr/n-Bu3N-catalyzed one-pot synthesis of dimethyl carbonate was proposed.

Cesium-phosphorous-silicon mixed oxide (Cs-P-Si oxide), a typical acid–base bifunctional catalyst, efficiently catalyzes propylene carbonate synthesis from CO2 and propylene oxide under supercritical conditions (8-10MPa). This catalyst contains no halogens and requires no additional solvents.A portion of the catalyst was eluted into the product solution during catalysis. It was also found that Cs3PO4, one of the species that may be eluted from the Cs-P-Si oxide, is an effective non-halogen homogeneous catalyst.