Design And Application Of Ionic Liquid-based Porous Organic Polymers For The Catalytic Conversion Of CO₂

As an abundant,low-cost,non-toxic and renewable C1 resource,it is of great industrial value and practical importance to realize the conversion of CO₂ to generate value-added chemicals.Among them,the cycloaddition of CO₂ with epoxide to produce cyclic carbonate is a successful industrial strategy.However,many industrial processes emit relatively low CO₂ concentrations of about 7%-15%CO₂（v/v）,and studies to achieve CO₂ conversion under low CO₂ concentration conditions similar to post-combustion flue gas are still rare.Current research has shown that porous organic polymers（POPs）can be designed and synthesized at the molecular level due to their extremely high specific surface area,tunable nano-porosity,and easy functionalization,and have great advantages in heterogeneous catalysis,while their porous structure is also conducive to the enrichment of CO₂ at low concentrations.In this thesis,a series of functionalized metal-free and environmentally friendly ionic liquid-based porous organic polymers were obtained by solvothermal radical polymerization of vinyl-functionalized monomers and post-modified by quaternary phosphonium or quaternization.The main research contents include:A series of porous organic polymers with different quaternary phosphonium salt units（triphenyl phosphonium chloride,tributyl phosphonium chloride,tricyclohexyl phosphonium chloride）were designed and prepared by post-modification.The target polymer catalysts were characterized in detail by solid-state ¹³C NMR,solid-state ³¹P NMR,XPS,SEM,TEM,EDS,XRD,FT-IR,TGA,N₂ adsorption and CO₂ adsorption,and these ionic liquid-based porous organic polymers have large surface area and hierarchical pore structure.They were able to show excellent catalytic performance in the cycloaddition reactions of CO₂ and epoxides at 60°C in the absence of metals,solvents and co-catalysts.Structural comparison of the catalysts showed that the catalytic activity of the catalysts increased with the increase of the spatial site resistance of the quaternary phosphonium units in the catalysts.This difference was more obvious when low concentrations of CO₂ was used in the reaction.The porous organic polymer containing tricyclohexyl phosphonium chloride unit（POP-Bn Cl-CP）catalyzed the cycloaddition reaction of low concentration CO₂ with epichlorohydrin efficiently and stably with 94%conversion and99%selectivity.Moreover,there was no significant loss of catalytic activity after five times of recycling,showing excellent recyclability.In addition,ionic liquid-based porous organic polymers（POP-PA-COOH,POP-PA-OH and POP-PA-NH₂）modified with different types of polar groups（carboxyl,hydroxyl and amino groups）were obtained by post-modified quaternary phosphonium reaction of vinyl-functionalized triphenylphosphine polymer POP-PPh₃,and the target polymer catalysts were characterized in detail.Under mild conditions,this series of porous organic polymer materials can be used as effective heterogeneous catalysts in the cycloaddition reactions of CO₂ with epoxides.The results showed that POP-PA-NH₂ had much higher catalytic activity than POP-PA-OH and POP-PA-COOH.When the reaction was carried out under low concentration of CO₂,this activity difference could be further amplified,and POP-PA-NH₂ had a conversion of 85%and a selectivity of 99%in 96 h.Furthermore,porous organic polymers（POP-Py-COOH,POP-Py-OH and POP-Py-NH₂）functionalized with different types of polar groups were obtained by a simple quaternization reaction of vinyl-functionalized pyridine polymer POP-Py,and the target polymer catalyst was characterized in detail.Under mild,solvent-free,metal-free and cocatalyst-free conditions,this series of ionic liquid-based porous organic polymer materials can be used as effective heterogeneous catalysts in the cycloaddition reaction of CO₂ with epoxides.The catalytic performance of POP-Py-NH₂ was slightly higher than that of POP-Py-OH and POP-Py-COOH,with a conversion of 81%and a selectivity of99%.When the reaction was carried out at a low concentration of CO₂,this activity difference can be amplified,with a conversion of 76%and a selectivity of 99%.Moreover,the catalyst also had good applicability to different epoxy substrates and exhibited slightly better recycling performance.