Arylimidazole Porous Organic Polymers Catalyze The Conversion Of CO₂ Into Formamide And Cyclic Carbonate

As climate issues continue to intensify,the realization of the“carbon neutrality”goal has become increasingly urgent.The conversion of CO₂ into high-value organic chemicals such as amides and cyclic carbonates to achieve resource utilization is of great significance for“carbon neutrality”.Catalysts are critical for the chemical conversion of CO₂.Porous organic polymers have been widely used to catalyze the chemical conversion of CO₂ in recent years because of their internal hierarchical pores and active sites,which can simultaneously have the ability of CO₂ capture and catalytic activation.However,it has been reported that porous organic polymers used for catalytic CO₂ conversion have some shortcomings,such as low stability of catalytic sites,difficulty in catalyst synthesis,and insufficient mild reaction conditions.In view of the above shortcomings,this topic intends to design arylimidazole porous organic polymers and carry out research on their catalytic performance for the conversion of CO₂ into formamide and cyclic carbonates.The main research contents and results are as follows:（1）Arylimidazole polyionic liquids catalyze the conversion of carbon dioxide into amide compounds.Under heating conditions,1-vinylimidazole reacted with 1,2-bis（bromomethyl）benzene to form a bidentate aryl imidazolium salt monomer（NL-2）.NL-2 was copolymerized with divinylbenzene（DVB）to obtain aryl imidazolium poly（ionic liquid）（POP-NL-2）.Further exchange of Br^-in POP-NL-2 for HCO₃^-,aryl imidazolium poly（ionic liquid）with HCO₃^-（POP-NL-2-HCO₃）was obtained.The characterization results showed that POP-NL-2 and POP-NL-2-HCO₃ had complete imidazole skeleton and rich pore structure.The specific surface areas were 421.0 m²/g and 449.9 m²/g,respectively.The average pore size was about4 nm.The maximum adsorption capacity of CO₂ under standard conditions was 18.4 cm³/g and 21.8 cm³/g,and it had thermal stability below 380℃.The catalytic performance of POP-NL-2 and POP-NL-2-HCO₃ for the conversion of CO₂ to formamide was studied under atmospheric pressure.The formylation reaction of CO₂ and benzamide was used as the model reaction.The reaction conditions such as temperature,alkali,reducing agent and solvent were optimized by single factor method.The optimum reaction conditions were as follows:The temperature was 25℃,the reducing agent was phenylsilane,acetonitrile was solvent and potassium tert-butoxide was added.Under the optimized reaction conditions,POP-NL-2 and POP-NL-2-HCO₃ have good catalytic effect on the target reaction,and the reaction yield were79%and 87%respectively,indicating that the introduction of HCO₃^-can improve the catalytic effect of the catalyst.Using POP-NL-2-HCO₃ as catalyst and different amides as substrates,21 kinds of formamide compounds were synthesized with reaction yields of56%-87%.Cyclic experiments showed that POP-NL-2-HCO₃ could be recycled at least 5times,and the model reaction was amplified by 20 times,and the yield was still 72%.（2）Pre-coordinated silver nanoparticles in N-heterocyclic carbene polymer efficiently fixes carbon dioxide in lime kiln waste gas.The tridentate aryl imidazolium salt monomer（NL-3）was synthesized by the reaction of1-vinylimidazole and 1,3,5-tris（bromomethyl）benzene,and then the metal silver was pre-coordinated to the monomer NL-3 to obtain a nitrogen heterocyclic carbene-silver metal complex（Ag@NL-3）.Then Ag@NL-3 was copolymerized with DVB crosslinking agent to synthesize a nitrogen heterocyclic carbene porous organic polymer（Ag@POP-NL-3）loaded with silver nanoparticles.The characterization results showed that Ag@POP-NL-3 has a complete imidazole skeleton structure,and silver nanoparticles with a particle size of 2-5 nm were distributed inside it.The specific surface area of Ag@POP-NL-3 was 382.8 m²/g,the average pore size is about 7 nm,and the maximum adsorption capacity of CO₂ was 11.3 cm³/g at room temperature and atmospheric pressure.And Ag@POP-NL-3 had thermal stability below 350℃.The catalytic performance of Ag@POP-NL-3 for the conversion of low concentration CO₂ in CO₂/N₂ mixture（CO₂ concentration=30 vol%）to cyclic carbonates was studied by using the carboxylation cyclization reaction of CO₂ and alkynol as a model reaction at room temperature and atmospheric pressure.The conditions of metal,ligand,alkali and reaction time were optimized by single factor method.When Ag@POP-NL-3 was used as catalyst,acetonitrile was used as solvent,DBU was used,and the reaction time was 12 h,the reaction effect was the best.Under the optimized conditions,10 cyclic carbonates were synthesized with 73%-99%yields.In addition,Ag@POP-NL-3 was successfully used as a catalyst to directly convert low-concentration CO₂ in the lime kiln waste gas into six different cyclic carbonates with a yield of 85%-95%.Cyclic experiments showed that the catalyst could be recycled at least 5 times,and the model reaction was amplified by 12 times,and the yield was still 90%.The catalyst can be recycled at least five times.Finally,the mechanism of carboxylation cyclization reaction of CO₂ and alkynol catalyzed by Ag@POP-NL-3 was proved by in-situ infrared spectroscopy and nuclear magnetic resonance spectroscopy.