Catalytic conversion of carbon dioxide into cyclic carbonates and fuels over metal ionic liquid complexes: Experimental and DFT studies

A series of metal ionic liquid complexes were prepared at ambient conditions, further applied as the highly-efficient catalysts for promotion synthesis of cyclic carbonates and fuels with CO2 as the starting material. The structural characteristics and inherent properties of all the complexes were respectively tested by various technologies (XRD, FT-IR, TG-DTG, NMR and NH3/CO2-TPD). Interestingly, the highest catalytic performance was found with 97.63 % of epichlorohydrin (ECH) conversion and 96.13 % of chloropropene carbonate (CPC) yield when the [1,1’-(butane-1,4-diyl)-bis(3-methylimidazolium)][MnCl4] (BMMnCl) was added in the coupling reaction at the optimal parameters (90 °C, 8h, 1.0 wt% catalyst of ECH, and initial pressure of 2.5 MPa). Importantly, the recyclable results showed that only a slight decrease in ECH conversion after five cycles, confirming that the catalytic performance of BMMnCl was stable during the coupling reaction. Besides, various epoxides were also applied as the coupling reagents for studying catalytic scope of BMMnCl in enhancement of CO2 conversion. Besides, when the photoreduction was performed for 4h under CO2 atmosphere (1 bar), the highest yield was observed over [1,1’-(butane-1,4-diyl)-bis(triethylaminonium)][CoCl4] (BTCoCl) (15.80 μmol g−1 h−1 of CO and 2.66 μmol g−1 h−1 of H2), which was confirmed by DFT calculations. Finally, the proposed reaction pathways of CO2 conversion were unveiled by DFT calculations.