The direct transformation of carbon dioxide to organic carbonates over heterogeneous catalysts

In this review article, we report the recent developments of heterogeneous catalysts for the synthesis of cyclic and dimethyl carbonates from CO₂ through various routes. The synthesis of cyclic carbonates via cycloaddition of CO₂ to epoxides is one of the few processes that have been commercialized. Compared to the many effective homogeneous catalysts, the heterogeneous catalysts have the advantages of being superior in stability and reusability. However, of the reported catalysts including metal oxides, zeolites, smectite, supported organic bases, metal complexes, and ionic liquids, none can be considered as highly active and selective under mild conditions. Also, heterogeneous catalysts used in other routes do not perform satisfactorily. The supported ionic liquids have attracted much more attention and are worthy of further research for the cycloaddition reaction. We predict that the mechanisms of acid-base or electrophile-nucleophile catalysis proposed in the literature will be valuable for the design and fabrication of high-performance catalysts.