Preparation Of Cyclic Carbonates From CO₂ And Epoxides Catalyzed By Multi-component To Single-component System

Due to the rapid development of industrialization,excessive carbon dioxide（CO₂）have been discharged,resulting in a series of environmental problems such as environmental pollution and greenhouse effect.With the proposed strategic goals of"carbon neutrality"and"carbon peaking",it is imperative to realize the balance of production and sales of carbon dioxide in human society and the natural environment.CO₂ is abundant,non-toxic,cheap and easy to obtain.As an important C1 resource,it is widely used in the synthesis of bulk chemicals and organic dyes to realize its high-value utilization.To date,CO₂ has been converted into many valuable chemicals.Among them,the preparation of cyclic carbonates from CO₂ and epoxides is a 100%atom-economical reaction,which is considered to be one of the feasible ways for carbon dioxide resource utilization.Cyclic carbonates can be used as battery electrolytes,aprotic polar solvents and fine chemical intermediates.However,because CO₂ is too stable,the cycloaddition reaction often requires high temperature and pressure,and in some systems,the catalyst is difficult to recycle and the catalytic efficiency is not high,which limit their large-scale production.In this dissertation,Zn-C₃N₄ composites and multifunctional biomass-based ionic liquids were prepared by introducing multi-active sites to achieve synergistic catalysis and used as catalysts for the cycloaddition reaction of carbon dioxide and epoxide to synthesize cyclic carbonates,respectively.Developed systems realized the transformation from multi-component to single-component catalysis.The dissertation mainly includes the following two aspects:（1）Based on the rich pore structure and multiple basic catalytic sites of C₃N₄,Zn-C₃N₄composite material was synthesized through two steps:melamine was calcined into a porous carbon nitride material（C₃N₄）,and then Zn active centers were introduced into C₃N₄.The Zn-C₃N₄ composite material was well characterized by FT-IR,EDS and other characterization methods.The results indicated that the introduction of metal Zn did not damage the basic skeleton structure of C₃N₄ and was evenly distributed on the surface.Using 5 mg of Zn-C₃N₄composite material as the catalyst and tetrabutylammonium bromide as the additive,up to95.1%yield from CO₂ and epoxdies was obtained under the conditions of 1 MPa CO₂ and100 ^oC for 4 h.（2）A series of new single-component multifunctional biomass-based ionic liquids were designed and synthesized from 5-hydroxymethylfurfural（5-HMF）as a biomass platform molecule,which were used for the cycloaddition of CO₂ and epoxides reaction.[HMF-NMe Et₂]I exhibited the highest activity.Under the conditions of 2 mol%[HMF-NMe Et₂]I,100 ^oC,and 0.5 MPa CO₂,the yield of cyclic carbonates was up to 95.0%for 6 h.An efficient,single-component,and metal-free system was developed,avoiding the usage of co-catalyst.The ionic liquid was easy to be separated and recycled,had high stability,and the yield did not drop significantly after 4 cycles.