Preparation Of Propylene Carbonate Catalyzed By Hydroxyl/Amine Ionic Liquid Supported Mesoporous Molecular Sieve

The development of environmentally friendly industries that utilize CO₂ has been one of the current research hotspots.CO₂ as a carbon source for conversion into useful compounds is a necessary approach.One of the most promising approaches in this field is the synthesis of five-membered cyclic carbonates from CO₂ and cyclic oxides.The reaction is characterized by the full utilization of CO₂ and the high atomic utilization.Ionic liquids as environmentally friendly solvents have good catalytic properties in terms of catalysis.Based on the problems that the separation of ionic liquids from products is relatively difficult,and the catalytic activity of heterogeneous catalysts is low and the reaction conditions are relatively harsh,in this paper,five-membered cyclic carbonates were prepared by using functionalized ionic liquids immobilized onto the carrier of mesoporous molecular sieves.Based on the designability of ionic liquids,this paper prepared the functionalized ionic liquids containing hydroxyl and amino groups:[APmim]Cl,[AP-bmim]Cl and[1-OH-3-NH₂-mim]Cl.The structures of the ionic liquids were characterized by IR and NMR,which showed that the functional ionic liquids were synthesized.The purity of the product was determined by non-aqueous titration method and the content of ammonia in the product was 0.85-0.92 mol NH₂/mol ILs.A series of heterogeneous catalysts were prepared by chemically bonding functionalized ionic liquids onto SBA-15 and MCM-41 for the cycloaddition reaction of CO₂ with propylene oxide.[1-OH-3-NH₂-mim]Cl/SBA-15 exhibited the superior catalytic performance.At the same time,it was found that with the increase of the length of the imidazole alkyl side chain,the catalytic performance was improved to some extent,and the addition of hydroxyl and amino functional groups significantly improved its catalytic performance.By changing the reaction conditions,the optimal reaction conditions were determined:the reaction temperature at 373 K,the initial pressure of CO₂ under 1.8 MPa,the reaction time in 4h,the amount of catalyst about 50mg,the conversion of propylene oxide was 90.4%,and the product selectivity was 92.5%.Meanwhile the cycle stability of[1-OH-3-NH₂-mim]Cl/SBA-15 was carried out and it was exhibited that the catalyst was reused only with significant loss of activity after numberous recycles.It was indicated that the heterogeneous catalyst could achieve the high catalytic performance with single-component under mild reaction conditions.Furthermore,catalysts and product could be quickly separated by simply filtering.The FT-IR and solid-state NMR characterization of[1-OH-3-NH₂-mim]Cl/SBA-15showed that the ionic liquid was successfully loaded on the mesoporous support.After elemental analysis,the catalyst loading was 0.75 mmol ILs/g.The SEM,BET,and XRD characterizations of mesoporous materials revealed that the framework structure of the molecular sieve did not change before and after the loading.The thermogravimetric analysis of TGA showed that the catalyst had good thermal stability at 303?.In this study,quantum chemical calculations on the reactant and active components were calculated by Gaussian at the B3LYP/6-311+G?d,p?basis set in DFT theory,optimizing geometry configuration and frequency,analyzing the topological properties of the composites,drawing electrostatic potential energy maps,calculating the frontier orbits of composites,the results showed that the addition of catalyst significantly reduced the difference of LUMO and HOMO between epoxide and CO₂,simultaneously,based on the AIM theory,the relationship between the catalytic activity and the molecular structure was preliminarily inferred.The hydrogen bond between-OH and-NH₂ between active components and propylene oxide promoted the ring opening of the epoxide,which was the decisive factor in the reaction.