Preparation Of Ionic Porous Organic Polymers And Research On Catalytic CO₂ Conversion To Cyclic Carbonates

CO₂ is the most important greenhouse gas,and its excessive emission can easily lead to many problems such as global warming,ocean acidification,and photosynthesis imbalance.At the same time,CO₂is also a non-toxic,easily available and cheap C1 resource.Therefore,the capture and utilization of CO₂is important for improving the ecological environment and fixing carbon resources.Among them,the reaction of CO₂with epoxides to prepare cyclic carbonates which shows a 100%atomic economy,and cyclic carbonates have many advantages such as high boiling point,high polarity,low volatility,degradability and solubility,thus this reaction has received widespread attention.However,the catalytic systems currently reported generally have defects such as difficult separation of catalysts or harsh reaction conditions.Therefore,it is crucial to design and construct novel catalytic materials with multiple active sites,high catalytic activity and easy separation and reuse.By designing the functional aldehyde amine monomers,a novel square amide porous organic polymer（SABA-POP）was prepared by hydrothermal method.Then,a series of squaramide-derived ionic porous organic polymers（SABA@EVIm-X,X=H,NH₂,OH,COOH）were constructed by post functional modification of SABA-POP by in-situ polymerization of vinyl ionic liquids and divinylbenzene and their structures were characterized.The effects of types of vinyl ionic liquids on the pore structure and stability of the catalysts were studied.The structural characteristics of constructed SABA@EVIm-X are rich N content,multiple hydrogen bond donors（HBD）and nucleophilic ion groups co-modification.The catalytic performance of the prepared catalysts in the CO₂cycloaddition reaction was studied,and the effects of reaction temperature,CO₂pressure,catalyst amount,and reaction time on the yield and selectivity of propylene carbonate（PC）were investigated.Epoxides with different substituents could be converted into corresponding cyclic carbonates at 120 ^oC,2 MPa,8 h without co-catalyst and solvent on SABA@EVIm-OH.In addition,the catalyst could be recycled for five times without significant changes in catalyst structure and activity.Based on SABA@EVIm-OH structure,the catalytic CO₂conversion mechanism synergistically between HBD and nucleophilic ion active centers was proposed.To introduce Lewis acid-base sites into the catalyst structures to further improve the catalyst activity,a series of pyridine-zinc based ionic porous organic polymers（Py-Zn@IPOP_X,X=Br,I,Ac）with multiple active sites were prepared through Schiff polycondensation and post modification strategy.The effects of different kinds of zinc compounds on the structures of catalysts were studied.Through the structural characterization of the catalysts,the catalysts have multiple active sites such as metal ions（Lewis acid）,nitrogen rich Lewis bases and nucleophilic groups.Using the cycloaddition of CO₂and propylene oxide（PO）to synthesize PC as a model reaction,the effects of catalyst structures and reaction conditions on catalytic activity were investigated.Py-Zn@IPOP_Icould efficiently catalyze the reaction of CO₂with PO to synthesize PC at 120 ^oC,2 MPa,5 wt.%,6 h without co-catalyst to obtain 96%PC yield and 99%selectivity.At the same time,the recyclability and universality of the Py-Zn@IPOP_Imaterial were investigated.The Py-Zn@IPOP_Istructure was remained intact after recycling for five times,and it exhibited high activity in the cycloaddition reaction of CO₂with different epoxides.Based on the Py-Zn@IPOP_Istructure and experimental results,the mechanism of Lewis acid-base synergistic catalytic cycloaddition reaction of CO₂and epoxides was proposed.For further simplifying the catalyst preparation process,a series of guanidine-derived ionic porous organic polymers（TCTB@Zn-iPOPs）were constructed by one-pot method,and their structures were characterized.The effects of metal content on structures of the catalysts were studied.The catalysts have the structural characteristics of rich nitrogen content and Lewis acid-base active sites co-modification.The TCTB@Zn-iPOPs materials were applied to the cycloaddition reaction of CO₂and epoxides.Through the research on the structural control of the catalysts,it was found that TCTB@Zn-iPOP-2 was the optimal catalyst.The reaction process conditions,cyclicity and universality of TCTB@Zn-iPOP-2 were investigated.The optimal reaction conditions were determined to be reaction temperature 130 ^oC,CO₂pressure 1 MPa,reaction time 5 h,and catalyst dosage 3 wt.%.Under this reaction condition,the activity of the catalyst was not significantly decreased after five cycles,and it exhibited excellent activity for catalyzing CO₂and epoxides with different substituents.The mechanism of Lewis acid-base synergistic catalysis for CO₂cycloaddition reaction was proposed based on the structure of TCTB@Zn-iPOP-2.