Incorporation of phenolic skeleton into imidazolium ionic polymers as recyclable catalysts for efficient fixation of CO2 into cyclic carbonates

Abstract

Developing a greener and efficient catalysts towards the direct fixation of atmospheric CO2 and then being used to synthesize high-value chemicals is of great interest, but challenging. To achieve this aim, rational design of the catalyst is very important. Herein, three imidazolium-based ionic polymers (IPs), named as IP 1–IP 3, are straightforwardly synthesized through a simple one-pot quaternization method by employing benzyl chloride linkers and tri-imidazole monomers (L1 and L2). These IPs are fully characterized using FTIR spectroscopy, 13C MAS NMR, XRD, elemental analysis, SEM with elemental mapping, HRTEM, TGA, XPS spectroscopy, nitrogen adsorption–desorption, and CO2/NH3-TPD methods. The newly synthesized IP 1 catalyst with phenolic hydroxyl shows an excellent catalytic activity toward CO2 cycloaddition with 97.1 % yield of cyclic carbonate under mild conditions (80 °C, 0.1 MPa CO2, solvent-free, 4.5 h). Moreover, the IP 1 catalyst is highly robust and can be reused at least for 7 consecutive runs. Mechanistic studies indicate that the synergic effect of hydrogen bonding and halogen anion in the IP 1 catalyst afford the ability to activate the substrate and ease the reaction kinetics, which results in an enhanced catalytic efficiency toward CO2 fixation. This work provides an efficient new method for the design and synthesis of multifunctional heterogeneous catalysts for the CO2 cycloaddition reaction.