CAS OpenIR
多位点离子液体催化合成环状碳酸酯的研究
时自洁
Thesis Advisor成卫国, 华炜
2020-07-01
Degree Grantor中国科学院大学
Degree Name硕士
Degree Discipline化学工程
Keyword环状碳酸酯, Co2, 环加成反应, 离子液体, 多活性位点
Abstract

作为温室气体的主要成分,CO2资源化利用成为了全球重要议题。环状碳酸酯的合成是固定转化CO2的原子经济性反应,产品环状碳酸酯应用广泛,需求量巨大。针对目前环加成反应中存在的均相催化剂难分离、非均相催化剂催化效率低于体相等问题,本文通过多活性位点离子液体设计以提高活性组分活性,继而分别通过负载与限域的方式分散活性位点以维持本征活性组分的活性,从而获得高催化活性的非均相催化剂。这为离子液体非均相化催化环加成反应提供了新的研究思路。主要工作及创新成果如下: 1.从活性组分高活性与高利用率的角度出发,设计合成具有不同结构的多活性位点的双中心离子液体。结合分析表征与活性评价,筛选出最优双中心离子液体[IMCA]2Br2,在130 oC,2.5 MPa下,碳酸丙烯酯的收率和选择性分别为97%和99%,催化活性优于单离子液体([IMCA]Br),且达到相同催化活性所需的用量仅为单离子液体的一半。 2.为实现活性位点的有效分散并保持本征催化活性,通过化学接枝的方式将筛选出的离子液体负载于SBA-15上。通过红外、热重、电镜等多种表征手段证明了离子液体的成功负载。实验结果表明,负载后的非均相催化剂[IMCA]2Br2@SBA-15具有最优的催化性能,催化环加成反应时碳酸丙烯酯的收率和选择性分别为97.4%和99.1%,催化活性几乎达到了体相离子液体的催化活性,离子液体本征高活性得以良好维持。通过DFT计算,结合表征分析等结果,提出羧基基团通过氢键作用与卤素阴离子协同催化的反应机理。 3.为将离子液体非均相化并保证本征结构完整性,采用最优的多位点离子液体[IMCA]2Br2作为模板剂一步合成了一系列限域不同离子液体量的催化材料,避免化学接枝占用材料硅羟基位点与束缚离子液体活性位点自由度。首先对比酸碱两种环境下限域离子液体的结构与性质,发现酸性环境下合成的0.2[IMCA]2Br2@mSiO2(H)和碱性环境下合成的0.2[IMCA]2Br2@mSiO2(OH)均表现出比体相离子液体更高的催化活性,这归因于限域后活性组分的结构完整性和离子液体活性位点的良好分散。其中酸性环境下合成的0.2[IMCA]2Br2@mSiO2(H)具有更大的比表面积且活性更高,是由于酸性环境更适用于羧基离子液体在硅源前驱体的有效分散。在所有制备的材料中,酸性环境下合成的0.6[IMCA]2Br2@mSiO2(H)表现出最佳的催化活性,碳酸丙烯酯的收率达到83.0%。;As the main component of greenhouse gas, the resource utilization of CO2 has become an important global issue. The synthesis of cyclic carbonates is an atomic economic reaction for the utilization of CO2. Cyclic carbonates are widely used in many fields. Aiming at solving the problems of homogeneous catalysts that are difficult to separate and the catalytic activity of heterogeneous catalysts need to be improved in cycloaddition reaction, ionic liquids with multiple active sites were designed to improve the activity and then the active sites of ionic liquids were fully dispersed by means of supporting or confining to maintain the activity of the intrinsic active component, thereby obtaining heterogeneous catalysts with high catalytic activity. This work provided a new idea for the heterogeneous catalyzed cycloaddition reaction of ionic liquids. The main work and innovations are presented as follows:1. From the perspective of high activity and utilization of active component, bicenter ionic liquids with multiple active sites and different structures were designed and synthesized. Based on the characterization and catalytic activity evaluation, the optimal bicenter ionic liquid [IMCA]2Br2 had the highest activity among all the prepared ionic liquids, achieving 97% yield and 99% selectivity of propylene carbonate under 130 oC, 2.5 MPa, which was better than that of single center ionic liquid ([IMCA]Br), and the amount was only half of the single center ionic liquid.2. In order to achieve effective dispersion of active sites and maintain the intrinsic catalytic activity, [IMCA]2Br2 was successfully supported on SBA-15 by means of chemical grafting. The successful supported of ionic liquids were then proved by various characterization such as FT-IR, TGA, and SEM. These materials were evaluated for cycloaddition reaction, the results showed that [IMCA]2Br2@SBA-15 presented the best catalytic activity among all the immobilized ionic liquids, achieving high yield (97.4%) and high selectivity (99.1%) of propylene carbonate, whose performance was almost able to reach the catalytic activity of equivalent molar bulk ionic liquids. The high intrinsic catalytic activity of ionic liquid could be maintained well. By characterization and DFT calculation, the synergistic mechanism based on hydrogen bond and halogen groups was proposed.3. In order to use ionic liquids as heterogeneous catalysts and ensure the integrity of intrinsic structure, [IMCA]2Br2 was used as template to synthesize mesoporous silica confined ionic liquids, avoiding the occupies of silicon hydroxy sites and the constraint of active sites. A series of materials were successfully synthesized for catalyzing cycloaddition reaction. The structures and properties of materials prepared using two methods were compared. The catalytic activity of 0.2[IMCA]2Br2@mSiO2(H) synthesized under acidic condition and 0.2[IMCA]2Br2@mSiO2(OH) synthesized under alkaline condition were higher than equivalent bulk ionic liquid, which was attributed to the integrity of intrinsic structure and good dispersion of the active sites. Among these two materials, 0.2[IMCA]2Br2@mSiO2(H) got a lager surface area and catalytic activity, possibly due to the acidic condition which was more suitable for the effective dispersion of ionic liquids in silicon source precursors. Among all the prepared materials, 0.6[IMCA]2Br2@mSiO2(H) showed the best catalytic activity, achieving 83.0% propylene carbonate yield. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/49715
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
时自洁. 多位点离子液体催化合成环状碳酸酯的研究[D]. 中国科学院大学,2020.
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