离子液体功能化MOFs复合材料的设计合成及其温和条件下高效催化转化CO2机制研究

In order to overcome the disadvantage in terms of the rigorous reaction conditions during the synthesis of cyclic carbonates through CO2 cycloaddition reaction, novel MOFs materials will be synthesis by combining the MOFs with numerous Lewis acid sites and ionic liquids with active groups as well as nucleophilic ions. The fabricated MOFs could efficiently catalyze the CO2 transformation under mild conditions. First, we will choose or design the MOFs whose metal centers contain proper electron density, then then anchor the task specific ionic liquid onto the MOFs framework via covalent chemical bonds to improve theirs catalytic activity. Meanwhile, in order to improve the mechanical strength and stability, MOFs will be loaded onto certain inorganic materials (as dispersed phase) or polymer matrix (as continuous phase) by in-situ synthesis method. Furthermore, the effects of the metal ion centers and ligands species, acid-basic properties, as well as ionic liquid species on the catalytic activity of the MOFs catalysts will be investigated in detail. In situ characterization and quantum computation will be used to clarify the catalytic mechanisms between the reactive centers and the substrates in terms of both experimental and theoretical viewpoints. Moreover, the intermediates and transition states during the cycloaddition reaction also will be studied by In-situ FT-IR and Raman, as well as quantum computation approaches. From the results, we will clarify the relationship between the structure and catalytic activity of catalysts, elucidate the role between the active site and substrates, and propose the reaction mechanism, which will be good evidences for design of more active MOFs in terms of both experimental and theoretical viewpoints.

针对CO2环加成合成环状碳酸酯反应条件苛刻等缺点，拟利用酸性位点丰富的MOFs材料与富含活性官能团和亲核离子的离子液体之间的耦合作用，研究在温和条件下实现CO2高效转化为环状碳酸酯的新型MOFs材料。以构建适宜电子云密度金属中心设计优选MOFs，利用后修饰改性的方法固载离子液体至其骨架，得到离子液体功能化的MOFs，并探索以无机或聚合物材料为增强或基体原位生长MOFs的方法和机制，以得到具有良好机械性能和稳定性的MOFs复合材料。系统考察金属中心和配体种类及性质、材料酸碱性、离子液体结构等对其活性的影响，利用原位技术监测反应中间产物，并借助密度泛函理论搜索出其过渡态，揭示降低反应活化能的规律、构建催化剂结构与性能之间的构效关系、明确活性中心与底物之间的作用机制，揭示反应机理。本项目将为高效CO2环加成催化剂的设计合成提供理论和实验依据，为工业废气CO2资源化利用和减排的同步实现提供新策略。

本项目以利用CO2与环氧化物通过绿色高效环加成反应合成环状碳酸酯为应用目标，针对环加成反应条件苛刻、传统多相催化剂活性低、长效性差等缺点，从CO2与环氧化合物等底物的活化本质出发，以具有丰富酸性位点、大比表面积和开放孔结构的金属有机骨架材料（MOFs）为反应载体，通过碳化复合、热处理活化、离子液体固载及聚离子液体复合等手段对MOFs活性中心进行调变、修饰和改性，构建了一系列高效能、长寿命的功能化多相MOFs催化剂，实现了环状碳酸酯高活性和高选择性合成。研究过程中首先设计合成了多类氨基（乙烯基、烷基溴、巯基）改性的新型离子液体和/或MOFs，再通过不同官能团间的配位键合、化学取代、聚合杂化等多重途径实现了离子液体对MOFs材料的功能增效和复合稳定化；证实了适宜强度和数量Lewis酸/碱中心、亲核物种等活性位点是提升催化剂活性的关键；利用原位FT-IR和DFT计算等手段探明了碳酸盐、醇盐等中间物种的存在，阐明了不同类型活性位点对底物的活化能力和机制，揭示了环加成反应的核心步骤及反应机理。通过项目的顺利实施研制出具有应用潜力的高效环加成多相催化剂，为催化剂的进一步优化设计及工业应用提供了丰富的理论和实验依据。