Ionic-Liquid-Based Polymers For Conversion Of CO₂ To Cyclic Carbonates At Ambient Pressure

Excessive carbon dioxide?CO₂?emission has been considered as one of the dominant factors that cause global warming and climate change over the past decades.As an abundant and non-toxic C1 resource,on the other hand,CO₂can be converted into high value-added bulk and fine chemicals.The chemical fixation of CO₂ under mild conditions,especially at atmospheric pressure and room temperature,is of vital importance both in terms of environmental protection and resource utilization.However,the inherent thermodynamic stability and kinetic inertness of CO₂ make it difficult to be activated,and the conversion of CO₂ under mild conditions is thus a great challenge.Ionic liquids?ILs?have attracted increasing attention in the fields of CO₂capture and conversion because of their unique properties,including high thermal stability,good CO₂ solubility,and,most importantly,tunable functionalization.However,the inherent disadvantages of homogeneous ILs like high viscosity,high mass transfer resistance and lack of multiple active sites,limit the effective improvement of catalytic activity in CO₂ conversion.The ionic liquid-based heterogeneous catalysts have the characteristics of both ionic liquid and heterogeneous catalyst,which can avoid high viscosity of ionic liquid,reduce the dosage of ionic liquid,and is easy to recover and separate.Herein,we prepared a variety of ionic liquid-based polymer catalysts via covalent polymerization and supramolecular assembly,which can efficiently capture and catalytically convert CO₂ at ambient pressure and low temperature without the help of any cocatalyst.The main researches and results are as follows:?1?A series of mesoporous poly?ionic liquid?-based heterogeneous catalysts with acid-base functionalized imidazolium ionic liquid as the main active component and quaternary ammonium ionic liquid as the cocatalyst,and their catalytic performances in the coupling reaction of CO₂ and epichlorohydrin were investigated.The synergy in the acid-base sites has been systematically tuned through varying the acid/base groups?amino-or carboxyl-?,counterions?Br^–,Cl^–,or OH^–?,and amount and molar ratio of imidazolium and quaternary ammonium ionic liquids.Due to the cooperation of multiple base-acid sites?Br^–,Cl^–,–NH₂,imidazolium ring?the resultant catalyst PADV-2can catalyze CO₂ into chloropropene carbonate with outstanding yield and selectivity at atmospheric pressure and low temperature?50°C?without the help of any cocatalyst.The PADV-2 catalyst can be easily recovered and recycled five times without loss of activity.?2?A series of supramolecular polymers?PAP-X?containing multifunctional active sites were prepared by dynamic covalent interaction between amino groups in amino-functional poly?ionic liquids?and aldehyde groups in terephthalaldehyde.Based on the pH sensitivity of dynamic covalent bond,the supramolecular assembly process can be regulated via adjusting the pH value of the solution,thereby effectively regulating the structural properties of the supramolecular polymers.As the pH increases from 9 to 12,the catalytic performance of PAP-X increases initially and then decreases.At pH=10,the catalyst PAP-1-10 can efficiently catalyze CO₂ into chloropropene carbonate with outstanding yield?94%?and selectivity??99%?at atmospheric pressure and low temperature?50°C?without the help of any cocatalyst.?3?To further improve the catalytic performance and stability of supramolecular polymer,the dual-amino functionalized ionic liquid DAIL and terephthalaldehyde was assembled in MIL-101 via dynamic covalent interaction to form a heterogeneous catalyst MIL-101-DP-X.It was found that MIL-101-DP-4 can efficiently catalyze the CO₂ into chloropropene carbonate?yield 97.5%,selectivity?99%?at ambient pressure and 50^oC.Compared to the linear supramolecular polymer,the catalyst exhibits excellent stability,the catalytic performance of which remains well after recycled for several times.The mild preparation method,excellent catalytic activity and stability endow the catalyst with high potential for industrial application.