The Cycloaddition Reaction Of CO₂ Catalized By Inoic Liquids And Porous Materials

With the development of human society,global consumption of fossil fuels increases greatly,leading to the rapid growth of carbon dioxide?CO₂?concentrations in our atmosphere.As one of the major contributors to undesired climate change and environmental problem,excessive CO₂ emissions have greatly affected our world.On the other hand,CO₂ is the most abundant renewable carbon source in nature and a necessary material for life and many industrial processes.Thus,efficient Chemical fixation and transformation of CO₂ into high-value chemicals is an excellent strategy for reducing CO₂ emissions and fully utilizing this cheap C1 source,which may benefit the sustainable development of our society.Therefore,chemical utilization of CO₂ as an alternative green carbonyl source has great significance for making commodity chemicals,flues and materials,and has attracted extensive attention of chemistry researchers.Unfortunately,carbon atom in carbon dioxide has the highest oxidation state,and it is very stable thermodynamically.Accordingly,the development of efficient catalysts for CO₂ activation and fixation has become the key research area in this field.Therefore,in this work,we designed and developed a series of efficient homogeneous and heterogeneous catalyst materials,and studied their activation mechanism for CO₂,and catalytic performance and action mechanism for cycloiddition reactions involving CO₂,which may provide significant scientific information for developing novel and environmental friendlly routes fo CO₂ utilization.The main research contents are as follows:?1?A series of 1,8-diazabicyclo[5.4.0]undec-7-ene?DBU?based ionic liquids?ILs?were prepared and applied for the cycloiddition of CO₂ with propargylic alcohols to produce a-alkylidene cyclic carbonates.The influence of ionic liquid type,reaction temperature,CO₂ pressure and reaction temperature on the reactions was investigated.It was found that the IL[DBUH][Mim]was very effective for catalyzing the reaction of propargylic alcohols and CO₂ without any solvent and co-catalyst.Moreover,the IL was easily recovered from the reaction mixture and then reused at least five times without loss of activity,thus homogeneous reaction of reactants and heterogeneous speration of catalyst were achieved.The interactions of IL with CO₂ and the substrates were examined by ¹H NMR,¹³C NMR spectroscopy and DFT calculations,and the catalytic mechanism of ionic liquids for the reaction was proposed.?2?Based on the synergistic activation for the reactions of CO₂ with propargylic alcohols,a highly efficient,green Cu?I?/IL catalytic system was designed and developed.The influence of copper salts and ionic liquid type on the reactions was investigated.It was found that different kinds of?-alkylidene cyclic carbonates could be produced at ambient temperature and pressure.After the completion of the reactions,the products were obtained in good to excellent yields by simple extraction separation,and the catalytic system could be easily regenerated without obvious loss in its activity.By NMR analysis and DFT calculations,the interactions of IL/CuI with CO₂ and the substrates were studied,and possible reaction mechanism was suggested.It was shown that the IL and CuI effiently active the hydroxyl and C?C triple bond of the substrate,respectively.As a result,the IL and CuI play a remarkable synergistic role in accelerating the reaction under mild reaction conditions.?3?A class of porous carbon supported noble-metal composite catalyst were developed,where the porous carbon with biomass-based coconut shell carbon and AgX?X=Cl,Br,I?were employed.The structure of the composite catalysts was confirmed by PXRD,FT-IR and SEM,and the catalysis of these composites on the cyclization reactions of propargylic alcohols with CO₂ was investigated.It was found that a range of propargylic alcohols could undergo the coupling reaction with CO₂ under conditions of atmospheric pressure and room temperature,and the yields of the desired products reached up to 99%under the optimized condition.The heterogeneous catalysts AgX@C could be easily recovered and reused at least ten times without loss of activity.Moreover,the product could be easily separated by simple solvent extraction.These findings resolved the problems of traditional post-separation process,such as product separation by column chromatography,low efficiency and difficulty in catalyst recovery.At the end,the effect of Ag salts with different structures on the reaction process was studied by DFT calculation,and the possible reaction mechanism was proposed.?4?According to the relationship between structure and performance,two kinds of imidazolium salts functionalized covalent organic frameworks?COFs?was designed and synthesized by pore surface engineering strategy.To analyze the structure of the obtained materials,powder PXRD,FT-IR,SEM,TEM,¹³C MAS-NMR,N₂ sorption isotherms and theoretical simulation calculations were conducted.The results showed that the resultant COFs possess high crystalline structure,high stability and surface area,and dense imidazolium ionic liquid on the pore walls.All the imidazolium ionic liquids functionalized COFs showed excellent catalytic performance for the cyclization reactions of CO₂ with epoxides under solvent-free and co-catalyst-free conditions.In comparison with the best transition-metal-free COF catalyst reported for this reaction,this type of materials developed in the present work displayed about 50-fold higher TON value?as high as 495000?under similar conditions.In addition,the material also showed remarkable selectivity and catalytic performance in the reductive N-formylation of amines with CO₂.The catalyst could be reused for at least ten times without significant loss of catalytic activity,and its high crystallinity and porosity were almost remained after the recycling.?5?Based on the designable and tunable characteristics of ionic liquids,a facile synthesis of two-dimensional multiple porous COFs?MP-COFs?in 1-alkyl-3-methylimidazolium tetrafluoroborates?[C_nmim][BF4],n=4,6,10?was reported at room temperature.The detailed structural characterization of the MP-COFs was performed by PXRD,FT-IR,SEM,TEM,¹³C MAS-NMR,and N₂ sorption isotherms.The as-synthesized MP-COFs exhibited high crystalline networks,permanent stability,and multiple pore size in one network.It was found that apart from the inherent pore as prepared by solvothermal approach,the size of pores in COFs could be simply tuned by adjusting alkyl chain length of the ionic liquids.Importantly,this general approach is applicable for the preparation of various MP-COFs,such as azine,imine,and hydrazone based COFs,which is rather difficult to acquire through traditional methods.In addition,these MP-COFs show superior catalytic performance,especially for large sized propargylic alcohols molecules based CO₂ transformtion reactions in comparison with unipore COFs.