The Preparation Of Ionic Liquid Post-modification Mofs Via Metal Coordination Bond And Its Application In CO₂ Fixation

A series of environmental problems caused by excessive CO₂ emissions have attracted much attention,and resource utilization of CO₂ is one of the important ways to reduce CO₂ emissions.The cycloaddition reaction of CO₂ and epoxides has become the main reaction of CO₂ chemical conversion because it conforms to the dual advantages of"green chemistry"and high atomic economy.Therefore,the key to the CO₂ cycloaddition reaction is to design an economical,stable and efficient catalyst.At present,as a porous material with high specific surface area,MOFs has been widely used in CO₂ cycloaddition reactions.However,most MOFs materials still need to be improved due to problems such as single active site and relatively harsh reaction conditions.In response to this problem,the introduction of other active sites to synthesize functionalized MOFs is a hot spot for cycloaddition reactions.MIL-101can be a good carrier because of its high specific surface area and pore volume.It can efficiently catalyze CO₂ by introducing ionic liquid with high activity for cycloaddition reaction.Based on the above situation,this subject is based on the reaction mechanism,synthesizes heterogeneous catalysts with multiple active sites through the unsaturated metal center?Cr?on MIL-101 supporting ionic liquid?ILs?with high catalytic activity.Through the experiment,the following conclusions are drawn:?1?The ionic liquid was gradually loaded on MIL-101 by a post-modification method.The metal?Cr?on MIL-101 has a coordination effect,which easily forms a Cr-N coordination bond with the N atom on the triethylene diamine?DABCO?,and another N atom on the DABCO can react with the 2-bromoethanol,finally obtaining MIL-101-IL.Then,under the condition of without cocatalyst,its catalytic performance as a heterogeneous catalyst for carbon dioxide and epoxides was investigated.The experimental results show that under mild reaction conditions?100^oC,1.5 MPa?,the yield of propylene carbonate reached 97%in only 40 minutes,.The yield and selectivity did not decrease after 5 cycles.MIL-101-IL has excellent catalytic activity and stable cycle performance.?2?Functionalized MOFs with multiple active sites were synthesized by simple post-modification of MOFs.The ZnBr₂ with relatively high catalytic activity was selected to react with the imidazolium salt to synthesize a functionalized ionic liquid?APIm?₂ZnBr₂.The Cr-NH₂ coordination bond is formed by the?-NH₂?on the ionic liquid and the metal unsaturated site?Cr?on MIL-101,so as to achieve the purpose of stably supporting the ionic liquid on the MOFs,and constructing a plurality of MIL-101-?APIm?₂ZnBr₂ heterogeneous catalyst at the active site.Under the good synergistic catalysis between Lewis acid,basic site and amino group and halide ion in?APIm?₂ZnBr₂.At 120 ^oC,1 MPa,1 h reaction conditions,the yield and selectivity of propylene carbonate were 97.3%and 100%,respectively,showing good catalytic performance.MIL-101-?APIm?₂ZnBr₂ has excellent recyclability compared to the difficult recycling of the homogeneous imidazolium salt ionic liquid,and the yield and selectivity of the product hardly change after 5 cycles.