Design of POSS-Imidazolium Supported Hybrids for the Conversion of Carbon Dioxide into Cyclic Carbonates

Abstract

Nowadays, the design of heterogeneous catalysts for the conversion of CO2 into useful chemical products is attracting the attention of the scientific community. The catalytic processes involving carbon dioxide as C1 feedstock are of growing interest for the sustainable development.1 The synthesis of cyclic carbonates by coupling CO2 with epoxides is one of the most interesting pathways for the conversion of carbon dioxide in terms of both atom economy and final products applications. Moreover, ionic liquids emerged as one of the most active catalysts for the production of cyclic carbonates starting from CO2 and epoxides.2 Herein, a series of heterogeneous catalytic systems bearing imidazolium salts as active sites will be presented. Imidazolium functionalized polyhedral oligomeric silsesquioxanes hybrids were designed and prepared in order to be employed as heterogeneous catalysts for the synthesis of cyclic carbonates from carbon dioxide and epoxides. According to literature,3 imidazolium modified silsesquioxanes (POSS-Imi) display improved catalytic performances compared to unsupported imidazolium species for the conversion of CO2. This behaviour has been ascribed to a proximity effect of imidazolium moieties surrounding the POSS nanocage structure.Herein, in order to combine the positive features of POSS-Imi catalyst and the advantages of heterogeneous catalytic systems, several imidazolium modified POSS units were covalently grafted onto two solid supports, namely amorphous silica (SiO2) and mesoporous SBA-15. All the solids were tested for the conversion of CO2 into cyclic carbonates by reaction with epoxides.