Synthesis And Catalytic CO₂ Conversion Of Triazine-derived Polyporous Organic Polymers

CO₂ is widely existed and continuously discharged in our daily life,causing a series of environmental problems such as global warming and sea level rise.At the same time,CO₂ is also a cheap,non-toxic,non-flammable and renewable source of carbon.Therefore,the chemical resource utilization of CO₂ has aroused widespread concern.Among them,the coupling reaction of CO₂ and epoxide is simpler and environmentally friendly than the traditional phosgene process,without any by-products,and its product cyclic carbonate was widely used in fine chemicals,electrochemistry,functional polymers and intermediates of drugs,showing a broad industrial prospect.However,the current catalytic system has defects such as cumbersome preparation process,low catalytic activity and poor structural stability.It is of great significance to develop new catalytic materials with high activity,high stability and easy separation and reuse.Firstly,the covalent triazine framework derived from square amide（CTF-SAM）was prepared by ionic thermal trimerization with zinc chloride as catalyst and solvent.The structure was characterized by FT-IR,solid ¹³C NMR,XRD,HR-TEM,N₂adsorption-desorption.CTF-SAM material has the structural characteristics of multiple dihydrogen bond donor and Lewis base active group comodification and high specific surface area.CTF-SAM material was used for CO₂ adsorption and catalytic conversion to synthesize cyclic carbonates.Through the study of structure regulation and structure-activity relationship of the material,it was found that the adsorptive capacity of the material to CO₂ can reach 1098-1586μmol/g at 273 K and 1 bar CO₂ pressure.The effect of different catalyst structures on the catalytic activity was studied,and the optimized CTF-SAM-CF₃/KI binary catalyst showed excellent synergistic catalytic performance for CO₂ cycloaddition reaction.Subsequently,the effects of different reaction temperature,CO₂ pressure,catalyst dosage and reaction time on the CO₂cycloaddition reaction were investigated,and the optimal catalytic reaction conditions were determined as follows:100 ^oC,2.0 MPa,5.0 h.In addition,under the optimized reaction conditions,the cyclic recycling performance of CTF-SAM-CF₃ catalyst and its universality to different epoxides were studied.The CTF-SAM-CF₃ catalyst could be recovered by simple centrifugation,and its activity did not significantly decrease after five cycles of use,and the catalyst showed excellent universality to different substituted epoxides.Finally,the reaction mechanism of reactant activation and cycloaddition reaction in the catalytic system was proposed.The CTF-SAM material was a bifunctional,structurally stable,and easily recycled mesoporous material,which opened up new avenues for CO₂ adsorption and catalytic conversion.Based on the principle of Schiff base polymerization,a series of metal-coupled triazine porous organic polymers（Zn@TFPOT-DAP）were constructed by designing different aldehyde-amine monomer structures,using ionic liquid as solvent and catalyst,and combining with post-modification method.The structural properties of the synthesized materials were studied by means of FT-IR,solid ¹³C NMR,N₂adsorption-desorption and SEM.The effects of different active sites on the catalytic coupling reaction of CO₂ and epoxide were investigated.The results showed that Zn@TFPOT-DAP had excellent catalytic activity.The effects of temperature,CO₂pressure,the amount of Zn@TFPOT-DAP and reaction time on the catalytic behavior have been systematically studied.Under the conditions of 90 ^oC,2.0 MPa,and 4.0 h,the yield of propylene carbonate（PC）can reach 98%,and its selectivity was 99%,realizing the heterogeneous catalytic conversion of CO₂.The reusability and versatility of Zn@TFPOT-DAP were investigated.Zn@TFPOT-DAP catalyst could be recovered by simple centrifugation.After five times of reuse,the activity of the catalyst was not significantly decreased,and the product was obtained with high yield for different epoxides.Finally,a reasonable catalytic reaction mechanism was proposed based on the multiple functions of Lewis acid/base sites and nucleophile groups.The synthesis method of porous organic polymers developed in this work was simple and green,showing broad development prospects in CO₂ cycloaddition reaction.