Functionalized Imidazolium Ionic Liquids Based Organic-inorganic Hybrid Materials For Efficient CO₂ Capture And Conversion

With the increasing greenhouse effect,the capture and conversion of CO₂has attached widespread attention in the scientific community.However,due to the high thermodynamic stability and kinetic inertia of CO₂,its chemical conversion often requires high temperature and high pressure,which restricts the industrialization process of CO₂ utilization.The development of ionic liquid-based organic-inorganic hybrid materials can significantly reduce the amount of ionic liquids,and the mass transfer resistance of CO₂,and then increase the adsorption/catalytic efficiency and recycling rate.However,there are still several disadvantages of ionic liquid-based organic-inorganic hybrid materials,such as the complicated immobilization processes,blocked pores of supports,and easy lose of ionic liquids.And most importantly,additional cocatalystsarestillinseparableduringcatalyticconversionunder low-temperature and low-pressure,making the current catalytic systems hard to be recycled.Herein,ionic liquid-based organic-inorganic hybrid materials with rich active sites,easy recovery,and high recycling rate have been constructed based on covalent grafting and supramolecular assembly method,so that direct reaction of CO₂ and epoxides to form cyclic carbonates under cocatalysts-and solvent-free and low temperature and pressure has been achieved.The detailed researches and results are given as follows:?1?Amino functionalized imidazolium ionic liquid?Mim-NH₂?and tetrabutylammonium bromide?TBAB?were physically mixed as catalyst and cocatalyst respectively to form a highly efficient binary homogeneous catalyst for cycloaddition of CO₂ and propylene oxide?PO?.The effects of molar ratio of catalyst/cocatalyst,CO₂ pressure,and reaction temperature on the yield of propylene carbonate?PC?were systematically investigated.It was found that Mim-NH₂ and TBAB have a good synergistic catalytic effect on CO₂cycloaddition,so that CO₂ can be converted efficiently under mild conditions in the absence of metal and solvent.Under n?Mim-NH₂?/n?TBAB?=1:1,75°C,and 0.35 MPa,the yield of PC reached up to 98.1%after reacted for 48 h.However,the homogeneous nature of this system makes it difficult for separation and recovery.Therefore,it is necessary to develop a heterogeneous catalyst by immobilizing ionic liquids on porous supports.?2?A bifunctional heterogeneous system combining both catalyst and cocatalyst was constructed through immobilizing binary ionic liquids,?amino-functionalized imidazolium and quaternary ammonium salts?on mesoporous cage-like material SBA-16.Under the excellent synergistic effect of the amino groups,halogen ions and the surface silanol groups,the composite exhibited outstanding catalytic activity for CO₂ cycloaddition reaction.Under mild reaction conditions?50°C,0.5 MPa?,the yield and selectivity of chloropropene carbonate could reach 98.5%and 99.6%,respectively.Furthermore,outstanding cyclic stability was shown by the composite,wherein the yield and selectivity of chloropropene carbonate were not noticeable decrease after recycling five times.?3?The CO₂ adsorbents ZIF-8-SFILs with multiple active sites were obtained through in-situ immobilizing the sulfonic functionalized imidazolium ionic liquids?SFILs?on metal-organic framework ZIF-8 based on the coordination interaction of the sulfonic acid group and Zn²⁺.The CO₂ adsorption properties of the resultant adsorbents in simulated flue gas?The volume ratio of CO₂ to N₂ is 15:85?at atmospheric pressure and different temperatures were studied.Under atmospheric pressure and 90°C,the CO₂ adsorption capacity of ZIF-8-SFIL-3 is 2.76 mmol?g^-1,which is 1.38 times that of pure ZIF-8.In addition,the adsorption performance of the adsorbent remained stable after 8cycles of adsorption-desorption.?4?A series of homogeneous catalysts MIL-101-CFILs containing both Lewis acid and basic active sites was prepared by in-situ immobilizing carboxyl functionalized imidazolium ionic liquids?CFILs?on metal-organic framework MIL-101 based on the coordination interaction of the carboxyl group and Cr³⁺,and used as catalysts for the cycloaddition of CO₂ and epichlorohydrin.The effects of reaction temperature and CO₂ pressure on the yield of chloropropene carbonate were systematically investigated.It was found that the Lewis acid and basic active sites in the catalyst have a good synergistic catalytic effect on the cycloaddition of CO₂,so that CO₂ can be converted efficiently under mild conditions in the absence of cocatalyst and solvent.High yield of 98.5%and selectivity of 99.2%of chloropropene carbonates were attained respectively under the optimal reaction condition?50°C,0.5 MPa,24 h?.The catalyst could be recovered and recycled easily,wherein a high catalytic performance was remained after being reused five times.