固载型季铵盐离子液体催化合成环状碳酸酯:烷基链长及羟基的影响（英文）

发布时间：2018-06-06 23:06

  本文选题：环加成反应 + 季铵盐　； 参考：《催化学报》2017年05期

【摘要】：CO_2是造成温室效应的主要原因,同时又是地球上储量最为丰富的可再生C1能源.因此,CO_2资源化受到了广泛关注.CO_2与环氧化物反应可合成环状碳酸酯,后者广泛用作极性溶剂、锂离子电池的电解液和聚碳酸酯中间体等.但是,由于CO_2的化学惰性,其反应需要高活性的催化剂.近年来,碱性金属、金属配合物及离子液体等均相催化剂被用于催化CO_2与环氧化物加成反应.其中,离子液体具有高热稳定性、低挥发性和结构可调性,得到了广泛研究.季铵盐、咪唑盐和季擕盐等离子液体已经被证实具有较高的催化活性.然而,均相催化剂回收困难,而且产物需要进一步纯化.将离子液体固载化制备成非均相催化剂,可以实现简单的固/液分离.聚合物、SiO_2、SBA-15、氧化石墨烯和羧甲基纤维素等固载化催化剂已经广泛用于CO_2和环氧化物的环加成反应.虽然非均相催化剂显示了潜在的优势,但是催化活性较低的问题仍然亟待解决,尤其是在较温和的反应条件下.因此,通过催化剂分子结构设计以提高催化性能,成为目前的研究热点.本文提出在催化活性基团和载体之间引入长烷基链,增加催化活性位点与反应物的接触面积,同时引入助催化的羟基,通过长链与羟基的协同作用,提高非均相催化剂活性.本文合成了羟基功能化长柔性链季铵化聚苯乙烯微球非均相催化剂([AHTAPC-PS]X,X=Cl,Br,I),用于催化CO_2与环氧化物的环加成反应,并与不含羟基的长烷基链季铵盐离子液体非均相催化剂([TAPB-PS]Br)及短烷基链季铵盐离子液体非均相催化剂([TMA-PS]X)的催化性能进行了对比.考察了固载后的离子液体烷基链长及侧链羟基对催化性能的影响,并通过实验和密度泛函理论计算研究了催化机理.红外光谱、扫描电镜和能量散射谱结果充分证明了季铵盐非均相催化剂的成功合成;热重测试表明,此类催化剂具有可以满足反应需求的热稳定性.密度泛函理论计算结果显示,与短烷基链非均相催化剂相比,长烷基链非均相催化剂的阴离子负电性更强,同时羟基与环氧化合物的氧原子之间存在强的氢键作用.羟基形成的氢键可以增加环氧化物的C O键长,同时强负电的阴离子更加容易攻击β-碳原子,促进环氧化物开环.另外,长烷基链结构使得卤素阴离子具有与反应物更大的接触范围,因此提高了反应活性.当采用短烷基链季铵盐非均相催化剂时,环氧丙烷(PO)与CO_2环加成反应生成碳酸丙烯酯(PC)的产率仅为70.9%,而采用长烷基链季铵盐非均相催化剂时产率可达91.4%(135°C,1.5 MPa,3 h),进一步加入助催化的羟基,则PC产率可提高到98.5%.此外,含羟基的长烷基季铵盐非均相催化剂在温和条件下也具有较高的催化活性(100°C,1.5 MPa,3 h,PC产率78.4%),该催化剂同时具有较高的循环稳定性(10次循环后,PC产率≥96%,选择性≥99%).综上所述,该催化剂具有优异的综合性能,展现了良好的工业应用前景.
[Abstract]:CO_2 is the main cause of Greenhouse Effect and the most abundant renewable C1 energy on earth. Therefore, the reaction of CO2 with epoxides has attracted much attention. The latter can be widely used as polar solvent, electrolyte for lithium ion batteries and polycarbonate intermediates. However, due to the chemical inertia of CO_2, its reaction requires highly active catalysts. In recent years, homogeneous catalysts such as basic metals, metal complexes and ionic liquids have been used to catalyze the addition of CO_2 to epoxides. Among them, ionic liquids with high thermal stability, low volatility and structural adjustable, has been widely studied. Quaternary ammonium salts, imidazole salts and quaternary salt-carrying plasma liquids have been proved to have high catalytic activity. However, homogeneous catalyst recovery is difficult and the product needs further purification. Heterogeneous catalysts were prepared by immobilization of ionic liquids to achieve simple solid / liquid separation. The supported catalysts, such as polymer SiO2 / SBA-15, graphene oxide and carboxymethyl cellulose, have been widely used in the cycloaddition reaction of CO_2 and epoxides. Although heterogeneous catalysts show potential advantages, the problem of low catalytic activity still needs to be solved, especially under mild reaction conditions. Therefore, the design of catalyst molecular structure to improve catalytic performance has become a research hotspot. In this paper, a long alkyl chain is introduced between the catalytic active group and the support to increase the contact area between the catalytic active site and the reactant. At the same time, the co-catalytic hydroxyl group is introduced to improve the heterogeneous catalytic activity through the synergistic effect of the long chain and the hydroxyl group. In this paper, hydroxyl functionalized long flexible chain quaternary ammonium polystyrene microsphere heterogeneous catalyst ([AHTAPC-PS] X _ (X _ (1) C _ (1) C _ (1) Br-B) has been synthesized to catalyze the cycloaddition reaction of CO_2 with epoxide. The catalytic properties of the catalyst ([TAPB-PS] Brand [TMA-PS] X) without hydroxyl group were compared with those of the non-hydroxyl chain quaternary ammonium salt ionic liquid heterogeneous catalyst ([TAPB-PS] Br) and the short alkyl chain quaternary ammonium salt ionic liquid heterogeneous catalyst ([TMA-PS] X). The effects of alkyl chain length and side chain hydroxyl groups on the catalytic performance of ionic liquids were investigated, and the catalytic mechanism was studied by means of experiments and density functional theory (DFT). The results of infrared spectra, scanning electron microscopy and energy scattering spectra fully proved the successful synthesis of quaternary ammonium salt heterogeneous catalysts, and the thermogravimetric test showed that these catalysts had the thermal stability which could meet the reaction requirements. The results of density functional theory (DFT) show that the anionic negative charge of the long alkyl chain heterogeneous catalyst is stronger than that of the short alkyl chain heterogeneous catalyst, and there is a strong hydrogen bond between the hydroxyl group and the oxygen atom of the epoxy compound. The hydrogen bond formed by hydroxyl groups can increase the C-O bond length of epoxides, and strongly negative anions can attack 尾 -carbon atoms more easily and promote the ring opening of epoxides. In addition, the long alkyl chain structure makes the halogen anions have a wider contact range with the reactants, thus increasing the reaction activity. When short alkyl chain quaternary ammonium salt was used as heterogeneous catalyst, Propoxypropane oxide reacted with CO_2 cycloaddition to produce propylene carbonate. The yield of propene carbonate was only 70.9, while the yield of long alkyl chain quaternary ammonium salt heterogeneous catalyst could reach 91.4 ~ 135 掳C ~ (1.5) MPa ~ (3) h ~ (-1). The yield of PC could be increased to 98.5% if the hydroxyl group was added further. In addition, the heterogeneous catalyst containing hydroxyl long alkyl quaternary ammonium salt also has high catalytic activity of 100 掳C ~ (-1) 1.5 MPa ~ (3) h ~ (-1) and 78.4% PC yields under mild conditions. The catalyst also has a high cyclic stability of 10 cycles and a PC yield of 鈮，

本文编号：1988486