Tonic Liquids With Multiple Sites For The Catalytic Synthesis Of Cyclic Carbonates

As the main component of greenhouse gas,the resource utilization of CO2 has become an important global issue.The synthesis of cyclic carbonates is an atomic economic reaction for the utilization of CO2.Cyclic carbonates are widely used in many fields.Aiming at solving the problems of homogeneous catalysts that are difficult to separate and the catalytic activity of heterogeneous catalysts need to be improved in cycloaddition reaction,ionic liquids with multiple active sites were designed to improve the activity and then the active sites of ionic liquids were fully dispersed by means of supporting or confining to maintain the activity of the intrinsic active component,thereby obtaining heterogeneous catalysts with high catalytic activity.This work provided a new idea for the heterogeneous catalyzed cycloaddition reaction of ionic liquids.The main work and innovations are presented as follows:1.From the perspective of high activity and utilization of active component,bicenter ionic liquids with multiple active sites and different structures were designed and synthesized.Based on the characterization and catalytic activity evaluation,the optimal bicenter ionic liquid[IMCA]2Br2 had the highest activity among all the prepared ionic liquids,achieving 97%yield and 99%selectivity of propylene carbonate under 130?,2.5 MPa,which was better than that of single center ionic liquid([IMCA]Br),and the amount was only half of the single center ionic liquid.2.In order to achieve effective dispersion of active sites and maintain the intrinsic catalytic activity,[IMCA]2Br2 was successfully supported on SBA-15 by means of chemical grafting.The successful supported of ionic liquids were then proved by various characterization such as FT-IR,TGA,and SEM.These materials were evaluated for cycloaddition reaction,the results showed that[IMCA]2Br2@SBA-15 presented the best catalytic activity among all the immobilized ionic liquids,achieving high yield(97.4%)and high selectivity(99.1%)of propylene carbonate,whose performance was almost able to reach the catalytic activity of equivalent molar bulk ionic liquids.The high intrinsic catalytic activity of ionic liquid could be maintained well.By characterization and DFT calculation,the synergistic mechanism based on hydrogen bond and halogen groups was proposed.3.In order to use ionic liquids as heterogeneous catalysts and ensure the integrity of intrinsic structure,[IMCA]2Br2 was used as template to synthesize mesoporous silica confined ionic liquids,avoiding the occupies of silicon hydroxy sites and the constraint of active sites.A series of materials were successfully synthesized for catalyzing cycloaddition reaction.The structures and properties of materials prepared using two methods were compared.The catalytic activity of 0.2[IMCA]2Br2@mSiO2(H)synthesized under acidic condition and 0.2[IMCA]2Br2@mSiO2(OH)synthesized under alkaline condition were higher than equivalent bulk ionic liquid,which was attributed to the integrity of intrinsic structure and good dispersion of the active sites.Among these two materials,0.2[IMCA]2Br2@mSiO2(H)got a lager surface area and catalytic activity,possibly due to the acidic condition which was more suitable for the effective dispersion of ionic liquids in silicon source precursors.Among all the prepared materials,0.6[IMCA]2Br2@mSiO2(H)showed the best catalytic activity,achieving 83.0%propylene carbonate yield.