Design And Synthesis Of Bifunctional Multiphase Catalysts Based On PILs For The Conversion Of CO₂

With the rapid development of the world economy,a large amount of energy consumption and excessive emissions have led to a sharp increase in the content of CO₂in the atmosphere.Therefore,how to effectively capture CO₂and its resource utilization has become a research hotspot in the field of green chemistry.A large number of studies have shown that the conversion path of generating five membered cyclic carbonates from CO₂and three membered epoxides through coupling reaction can effectively fix CO₂to achieve 100%atom economy efficiency.At present,various catalytic systems used to catalyze CO₂coupling reaction generally have problems such as harsh reaction conditions,low catalytic activity and difficulty in recycling.Therefore,it is of great research significance and economic and social benefits to develop a new and efficient heterogeneous catalyst with mild reaction conditions and good structural stability.Previous studies have shown that binary catalytic systems containing hydrogen bond donors and（or）acid base sites can effectively catalyze the cycloaddition reaction of CO₂with epoxides.The general catalytic mechanism is that hydrogen bond donors or acidic sites interact to activate epoxides,while nucleophilic sites at basic sites attack the cyclic carbon atoms of activated ternary epoxides to open their rings and promote carbon dioxide insertion.Inspired by this,we designed and synthesized three catalysts containing acid and/or basic sites for the coupling reaction of CO₂and epoxides based on the excellent catalytic activity of poly（ionic liquids）,including:（1）The porous organic polymers were prepared from tetravinylphenylporphyrin and 4-（diphenylphosphine）-styrene monomer by solvothermal reaction,and then were modified by metal and haloalkane after synthesis to obtain a metal porphyrin/quaternary phosphonium salt cross-linked poly（ionic liquids）bifunctional catalyst.The structure and performance of the catalyst were studied by ¹H,¹³C NMR,FT-IR,N₂adsorption desorption,NH₃/CO₂-TPD and other means.The isotherm of CO₂adsorption showed that there was a strong interaction between the catalyst and CO₂.The results showed that the metal porphyrin/quaternary phosphonium salt poly（ionic liquids）bifunctional catalyst（with a phosphonic compound to porphyrin feed ratio of 12）could achieve quantitative conversion of epichlorohydrin（ECH）at 90°C,0.1 MPa CO₂for 48 hours.The catalytic activity was improved by increasing the percentage of phosphonium salt content,the alkyl chain length of phosphonium salt,and the Lewis acidic strength of the ligand metal.The catalysts have good structural stability and recyclability and exhibit good catalytic activity and high selectivity for various epoxy substrates containing different substituents.（2）Methyl salicylaldehyde-4-vinyl diphenylphosphonium salt homopolymer was used as the main chain and cross-linked with ethylenediamine by Schiff base reaction and then ligated with metal to prepare catalysts containing metal and quaternary phosphonium salt as double active sites.The successful preparation of catalyst structures was demonstrated by ¹H,¹³C NMR,FT-IR,and XPS.The catalyst structure containing acid-base sites was determined by NH₃/CO₂-TPD means.The results showed that the bifunctional catalyst achieved 86%conversion of ECH at 80°C and 0.1 MPa CO₂for 24 h.The catalyst used could be recovered by simple filtration at the end of the catalytic reaction,and the catalytic activity was slightly reduced after four repeated uses.The catalyst showed good catalytic performance and high selectivity for various epoxy substrates.（3）Amino-functionalized imidazolium salt homopolymer was chosen as the main chain and triazine group was used as the cross-linking agent for the bifunctional catalyst of hydrogen bond donor/triazine group cross-linked polymer.The successful preparation of the catalyst structures was demonstrated by ¹H,¹³C NMR,FT-IR and XPS.The catalytic performance of the bifunctional catalysts was investigated and the effect of reaction conditions on the catalytic activity was examined.The results showed that the metal-free hydrogen bond donor/triazine based cross-linked poly（ionic liquids）bifunctional catalyst could achieve 94%conversion of ECH in the presence of 100°C,0.1 MPa CO₂,no co-catalyst and organic solvents for 24 h.The catalyst was also highly suitable and selective for various ternary epoxy substrates with different substituents.In summary,three bifunctional multiphase catalysts,metal porphyrin/quaternary phosphonium salt cross-linked poly（ionic liquids）,metal Salen/quaternary phosphonium salt cross-linked poly（ionic liquids）and hydrogen bond donor/triazine based cross-linked poly（ionic liquids）,were prepared and used to catalyze CO₂cycloaddition reaction by integrating multiple active sites in the same backbone.