Study On Catalytic Conversion Of Carbon Dioxide By Ionized Organic Porous Polymers

Global warming caused by greenhouse gas emissions is one of the most serious threats to human society and the natural environment,and CO₂ is considered to be the most important greenhouse gas.Therefore,how to efficiently convert CO₂ into other high value-added chemicals has very significant.Many homogeneous catalysts such as ionic liquids have been used to efficiently catalyze the conversion of CO₂,but because of their high viscosity and difficult separation,they have certain limitations in their use.Therefore,heterogeneous catalysts have great development prospects.In this thesis,a series of ionized organic porous polymers are designed and synthesized for the efficient conversion of heterogeneously catalyzed CO₂.First of all,polyimidazolium salts are an important class of catalysts used to catalyze the cycloaddition reaction of epoxides and CO₂.However,the synthesis process usually requires an initiator such as azobisisobutyronitrile or a metal catalyst to promote it.Therefore,t here is still a great need to develop a clean and environmentally friendly route to synthesize polyimidazolium salts.In this study,1,3,5,7-tetrakis（4-imidazolylphenyl）adamantane and halogenated hydrocarbons of different chain lengths 1,4-bis（bromomethyl）benzene,4,4’-bis（bromomethyl）-1,1’-biphenyl and 1,4-bis（bromomethyl）naphthalene were polymerized by a nucleophilic substitution reaction to synthesize three heterogeneous catalysts 2-5,2-6 and 2-7.They all show high stability and can efficiently catalyze the cycloaddition reaction of CO₂with epoxides.The experimentals result show that different chain length linking groups have important effects on the structure and catalytic properties of the polymer.Among them,catalysts 2-6 show the best catalytic activity,and can efficiently catalyze the reaction of CO ₂with various epoxides to form cyclic carbonates.Secondly,hydrogen-bonded donor catalysis has become an important method for metal-free activation of organic molecules.Although powerful,there are few reports on the use of hydrogen-bonded donors to catalyze CO₂ reactions.In this study,we take2,4,6-triethynylaniline 3-8 and 1,1’-bis（4-bromophenyl）-4,4’-bipyridinium chloride 3-5 as raw materials,polymers 3-9 containing a large amount of primary amines（-NH₂）were synthesized by Zincke reaction,The polymer 3-9 is then reacted with 3,5-bis（trifluoromethyl）isothiocyanate 3-10 and 3,5-bis（trifluoromethyl）isocyanate 3-11 respectively under very mild conditions.Introducing thiourea and urea structures into porous polymers,bifunctional polymers 3-12 and 3-13 containing dihydrogen-bonded donors were synthesized.These polymers are used to catalyze the cycloaddition reaction of CO₂ and epoxides.The experimental results show that the catalysts 3-12 and 3-13 have higher catalytic activity than3-9.The hydrogen-bonded donor is able to activate the epoxide,thereby improving the catalytic activity.In addition,the heterogeneous catalyst synthesized in this thesis has good stability,shows excellent recoverability,and its catalytic capacity does not decrease significantly after repeated recycling.