Supported Catalysis in Carbon Dioxide Activation

The use of carbon dioxide as a raw profitable material involves its integration in a chemical process using as mild reaction conditions as possible, which necessarily requires the use of a catalytic process. The incorporation of CO2 in cyclic carbonates by condensation with epoxides is a suitable process for that purpose. If a large scale process is the pursued objective, homogeneous catalysts proposed must be transformed in heterogeneous ones with high activity in order to simplify reaction conditions and, mainly, product isolation processes. The proposed catalysts, ranging from simple tetraalkylammonium salts or ionic liquids to salen or porphyrin metal complexes, can be supported on polymeric or inorganic matrices via covalent grafting. Due to the salt nature of some catalysts, simple adsorption on supports is also possible. Each catalytic system has specific reaction characteristics, needing or not a co-catalyst or a solvent. The support plays an additional role on the catalytic process; the existence of porosity in some cases as well as the presence of functional groups can create synergies with catalysts, and therefore improve catalysis enhancing the efficiency of the process compared with non-supported catalysis. In this review, recent progresses for the synthesis of cyclic carbonates from CO2 and epoxides will be described, particularly the aspects related to the reaction conditions and the efficiency of the system. Also, the same kind of parameters is analyzed in the use of supported catalysts for the preparation of oxazolidinones using CO2 and aziridines as reagents.