Study Of Ionic Liquid Functionalized MCM-41 Multiphase Catalytic CO₂ Cycloaddition Reaction

The resource utilization of greenhouse gas CO₂is an essential way to achieve the goal of"double carbon",which is of great strategic significance for addressing global climate change.The reaction route of chemically transforming CO₂and epoxy compounds to produce high value-added chemical products,cyclic carbonate,is in line with the concept of"green chemistry"and"circular economy"because of the low price of substrate raw materials and 100%atomic utilization rate of the reaction.At present,scientific researchers have developed a variety of catalysts for catalyzing the CO₂cycloaddition reaction.Among them,ionic liquids as homogeneous catalysts have high catalytic activity for this reaction,but there are problems of easy separation from the products and high viscosity,and multiphase ionic liquids are an important way to solve this problem.In this paper,a series of ionic liquid-functionalized MCM-41 heterogeneous catalysts were prepared by post-synthesis modification method,using silane coupling agent to immobilize quaternary ammonium salt ionic liquid and imidazole ionic liquid on the surface of MCM-41 molecular sieve respectively,and were used for CO₂cycloaddition.Their physicochemical properties of the catalysts were analyzed by XRD,EA,FT-IR,BET,SEM and TGA.The effects of reaction temperature,reaction pressure,reaction time and catalyst dosage on the catalytic activity were studied;the cyclic stability of the catalyst,its universality to epoxide substrates,and its catalytic activity at low CO₂concentrations were evaluated;the mechanism of catalyst-catalyzed CO₂cycloaddition reaction was proposed.The characterization results showed that the quaternary ammonium ionic liquid and imidazole ionic liquid were successfully solidified onto the surface of MCM-41 molecular sieve by post-synthetic modification,and the resulting ionic liquid functionalized MCM-41 had good thermal stability.The results of catalytic performance evaluation showed that the two types of ionic liquid functionalized MCM-41 catalysts produced showed good catalytic activity when used to catalyze the cycloaddition reaction of CO₂with propylene oxide（PO）to propylene carbonate（PC）;the quaternary ammonium ionic liquid functionalized MCM-41 catalyst（MCM-41-N/CH₃（1:3））could achieve 92.5%yield and 96.6%selectivity of PC at 140℃,2.0 MPa,3 h,and 15 wt%catalyst dosage;and the imidazole ionic liquid functionalized MCM-41 catalyst（MCM-41-Imi/COOH）could achieve 96.4%yield and 97.8%selectivity of PC at 120℃,2.0 MPa,4 h and 10wt%catalyst dosage.Both catalysts exhibited good cycling stability and epoxide substrate versatility.Two types of ionic liquid functionalized MCM-41 catalysts produced exhibited good cycling stability and epoxide substrate versatility.When applied to simulate the cycloaddition reaction of low-concentration CO₂（20%CO₂,80%N₂）in flue gas and epoxides,both catalysts have good catalytic activity.The PC yield of MCM-41-N/CH₃（1:3）was 78.8%,and the PC yield of MCM-41-Imi/COOH was 81.6%.