Preparation Of Cooperative Catalysts With Zinc And Ionic Liquids And Their Application In CO₂ Conversion

The preparation of cyclic carbonates by using CO₂ is a green sustainable development reaction,which not only utilizes CO₂,but also produces cyclic carbonates which have important application value in many aspects.Numerous studies have shown that the synergistic catalysis of zinc and ionic liquids can promote the cycloaddition reaction of CO₂ with epoxides.Based on the preliminary work,the cooperation catalyst containing ionic liquid and zinc was prepared.To achieve the the easy separation and recycling of catalysts,immobilization the ionic liquid on the mesoporous material is one of the easiest and most efficient method.Therefore,the bimodal mesoporous silica?BMMs?was used as the carrier to design and synthesize the cooperation catalyst of ionic liquid and zinc.Moreover,the cooperation catalytic mechanism of heterogeneous catalysts was proposed by studying the catalytic kinetics and the results obtained are as follows:?1?The ionic liquid of bromine/chloropropyl-1-methylimidazole were prepared to investigate the cooperation effect of different zinc salts on the cycloaddition reaction.The catalytic activities were promoted greatly by addition of zinc salt,and Zn?OAc?₂ showed the best synergistic effect with ionic liquid.The effects of catalytic reaction conditions and the molar ratio of zinc to ionic liquid?Zn/ILs?on the cycloaddition reaction were investigated.The results show that as the molar ratio of Zn/ILs increases,the catalytic activity decreases.?2?Immobilization catalysts containing both IL and Zn?BMMs-Zn&IL?were prepared using BMMs as carrier,through grafting of Zn?OAc?₂ and 1-?trimethoxysilyl?propyl-3-methylimidazolium chloride.The molar ratios of zinc to ionic liquid?Zn/IL?in heterogeneous catalysts could be adjusted by altering the amount of Zn?OAc?₂ and1-?trimethoxysilyl?propyl-3-methylimidazolium chloride in the initial system.Many characterization,including FT-IR,XRD,ICP,SEM,TEM,N₂ adsorption and desorption,were employed to investigate the composite and structure of BMMs-Zn&IL.The results indicated that the mesoporous structure of BMMs after loading zinc and ionic liquids were maintained with zinc in the form of Zn ²⁺,and the ionic liquid was grafted on the BMMs by covalent bonding.?3?The catalytic effect of the supported heterogeneous catalyst BMMs-Zn&IL was further studied.The catalytic activity increased with the increase of the molar ratio of zinc to ionic liquid.BMMs-Zn&IL-1.70 showed the highest catalytic activity?yield 98%,selectivity 97%?.As a comparison,the catalytic systems of ILs with Zn?OAc?₂,BMMs-IL with Zn?OAc?₂ and BMMs-Zn with ILs were studied,and the totally different catalytic effect and trend were presented,inferring the different cooperation behavior from BMMs-Zn&IL.In addition,the catalytic performance of BMMs-Zn&IL-1.70 on other epoxides was studied.At the same time,the cycle performance of the catalyst was tested.After the catalyst was cycled for 5 times,the high catalytic activity was still maintained.?4?The reaction kinetics of heterogeneous and homogeneous catalysis were studied.The apparent rate was obtained by the relationship between conversion rate and time.Then,the apparent activation energy?Ea?was calculated according to the Arrhenius equation.Among them,BMMs-Zn&IL-1.70 has the lowest apparent activation energy of 54.95 kJ/mol,which is consistent with the catalytic effect.The mechanism of synergistic catalytic reaction of homogeneous and heterogeneous catalysis are further proposed,inferring that the cooperation catalytsis of heterogeneous catalyst is more efficient than that in the homogeneous system,due to the confinement of nanopore.