Research progress of homogeneous and heterogeneous catalysts in CO₂ cycloaddition reactions

Carbon dioxide (CO₂) is a major anthropogenic greenhouse gas produced by chemical, thermoelectric and steel industries as well as transport sector. The increasing concentration of CO₂ in atmosphere is responsible for plenty of environmental problems such as global warming, rising sea levels and increasing global temperatures. However, CO₂ could consider as renewable, cheap and non-toxic chemical raw material, using CO₂ to produce high value-added chemicals to reduce carbon concentrations is a highly desirable strategy. Five-membered cyclic carbonates have a wide range of applications due to their superior physicochemical properties such as high boiling point, high dipole moment and biodegradability. The synthesis of cyclic carbonates from epoxides and CO₂ is by far the most approved method. Nevertheless, due to high thermal stability and kinetic inertness, it is necessary to activate CO₂ as feedstock for organic synthesis with large energy, which may result in the release of more CO₂ than is actually. Therefore, the use of CO₂ as C1 building block is long-term challenged. This paper outlines the progress of research on various types of homogeneous and heterogeneous catalysts for CO₂ fixation to generate cyclic carbonates, including organocatalysts, ionic liquids, metal-organic frameworks, and porous organic polymers. Almost all of these catalysts are currently available for the successful fixation of CO₂ to terminal epoxides on laboratory scale using pure CO₂ at ambient temperatures. For internal epoxides higher reaction conditions are usually required to achieve the desired conversion. It was analyzed three areas of present major challenges in catalyzing multi-substituted epoxides or bio-derived epoxides, diluted CO₂ conversion and industrialization, and the directions for future research efforts on the subject were suggested.