Preparation And Research Of Several Ionic Liquid Catalysts For Chemical Fixation Of CO₂

Global warming caused by the emission of greenhouse gases（such as CO₂）is a problem that all mankind needs to solve urgently.CO₂ capture and utilization（CCU）is one of the effective ways to reduce greenhouse gas emissions on a global scale.It is an ideal method to synthesize cyclic carbonate with epoxide and CO₂under certain conditions.The excellent properties of ionic liquids are in line with the conditions of being a catalyst for the cycloaddition reaction.In this paper,different ionic liquid catalysts were prepared by grafting and modifying ionic liquids to catalyze the synthesis of cyclic carbonates from epoxide and CO₂.The main content of this article is as follows:（1）Alkanolamine ionic liquids are grafted onto chloromethyl polystyrene microspheres through alkylation reaction and a simple one-pot method to form hydroxyl-functionalized quaternary ammonium salt ionic liquids on the surface of the microspheres.The effects of different anionic groups（Cl^-,Br^-,I^-,BF₄^-）on the reaction were compared.In order to explore the influence of reaction conditions,the catalyst dosage,reaction pressure,temperature and time,and other factors were studied,which can be used repeatedly.The cycloaddition reaction was determined to be a second-order kinetic reaction through kinetic studies,and the apparent activation energy of four different anionic catalysts was calculated.At the same time,density functional theory（DFT）was used to optimize the structure of the catalyst and propylene oxide molecule.Based on the experimental results and the DFT calculation results,the possible reaction mechanism of the reaction can be obtained reasonably.（2）Bipyridine and tetrabromotoluene synthesized 3-5 um ionic liquid polymer microspheres（TBB-Bpy）containing a large amount of anionic bromine by alkylation reaction and simple solvothermal method.Alcoholamine,imidazole,or pyridine was grafted onto the microspheres,and the catalytic activity of different supported ionic liquid catalysts was studied.After comparative experiments,pyridine-supported ionic liquid polymer microspheres（TB-Py）are the most active catalyst for the synthesis of cyclic carbonates from epoxides and CO₂,and density functional theory（DFT）is used to simulate different catalysts.Optimizing the structure of the catalysts and exploring the influence of Millikan charge and molecular structure on catalytic activity.Various factors affecting the activity of the TB-Py catalyst were discussed,such as reaction temperature,pressure,time,and catalyst dosage.Under milder reaction conditions,the yield of propylene carbonate reached expectations,the catalyst was reusable and easy to separate,and a possible reaction mechanism was proposed.（3）Ui O-Bpy was synthesized by the solvothermal method,and then by adding iodomethane and copper bromide again through the solvothermal method,Ui O-Bpy was quaternized and loaded with copper ions.Zr and Cu act as Lewis acid sites,and I^-acts as a halogen anion for the nucleophilic attack,forming a trifunctional metal-organic framework catalyst.After the modification,the activity of the catalyst was significantly improved,and the structure of the catalyst before and after the modification was studied using FT-IR,SEM,XPS,BET,TGA,XRD,and other characterizations.Under high temperature and high pressure,it can catalyze the synthesis of cyclic carbonate from epoxide.Adding cocatalyst can also catalyze the reaction under normal temperature and pressure.At the same time,the possible reaction mechanism is proposed.