Rational engineering of single-component heterogeneous catalysts based on abundant metal centers for the mild conversion of pure and impure CO2 to cyclic carbonates

Abstract The development of fully heterogeneous catalysts for the widely investigated cycloaddition reaction of CO2 to epoxides is crucial to achieve the sustainable synthesis of cyclic organic carbonates as useful emerging intermediates and building blocks. Nevertheless, relatively few fully heterogeneous catalytic systems exist for the title reaction with the ability to convert CO2 to carbonates under atmospheric pressure and mild temperatures especially when using diluted and/or impure CO2 as found in real case scenarios. Moreover, such catalysts are generally constituted by organic or metal-organic frameworks whose preparation generally involves the use or synthesis of expensive building blocks. In this work, we devised a convenient strategy to prepare single-component heterogeneous catalysts based on readily available metal halides and quaternary ammonium halide-based ionic liquids that started from a systematic evaluation of the corresponding homogeneous binary catalysts. This was followed by the preparation of silica-supported heterogeneous systems with different loadings of both catalytic components whose nature and composition were carefully studied through several characterization techniques (elemental analysis, FT-IR, ICP-OES, SEM and TEM microscopies, TGA analysis and XPS). The thus prepared catalysts showed the ability to carry out the cycloaddition of CO2 to several epoxide under atmospheric pressure at mild temperatures (25-40 °C) including when using diluted CO2 mixtures resembling low-calorific landfill gas with or without poisoning additives (H2S). Finally, the fate of the catalysts after reaction and their deactivation through the catalytic cycles is discussed.