钛掺杂乙基桥联型介孔分子筛的合成及催化环己酮氨肟化

发布时间：2018-05-11 13:45

  本文选题：钛掺杂 + 乙基桥联　； 参考：《华东理工大学》2017年硕士论文

【摘要】：钛掺杂有机基团桥联型介孔分子筛(Ti-PMO)是一类新型的介孔材料,不仅具有常规无机介孔分子筛的均一孔径、高比表面积和孔容等优点,而且其桥联的有机基团均匀分布在介孔骨架中,能够保护Si-O-Si键不被水解,因而具有出色的水热稳定性和疏水性。因此,Ti-PMO在一些大分子液相氧化反应中具有潜在的应用前景。尽管普遍认为含钛分子筛中孤立的骨架四配位钛是一些选择性氧化反应的活性中心,但活性位的确切性质仍存在争议,尤其是有越来越多的文献报道骨架中的四配位钛物种并不是唯一的活性中心。本文首先以商业TS-1为催化剂优化环己酮氨肟化反应工艺条件,为后续合成的介孔分子筛的考评提供依据。为了使反应过程中环己酮、H_2O_2和NH3三者的浓度较好匹配,并保持反应在碱性条件下进行,氨水采用间歇等份的进料方式。优化后,环己酮、氨水和双氧水的摩尔比为1:2.5:1.25。其次以TiCl3为钛源合成了具有良好的水热稳定性的钛掺杂乙基桥联的有机杂化介孔(Ti-EPMO)分子筛,系统考察了无机盐添加量、晶化温度、溶液酸度、硅源预水解时间和硅钛比等合成工艺条件对分子筛的物化性质的影响,并以环己酮氨肟化反应作为探针反应考评了其催化性能。结果表明无机盐是Ti-EPMO形成二维六方介孔结构的重要因素,而温度、酸度和硅钛比对分子筛中钛含量和钛配位形式的影响较大,当无机盐添加量为Si摩尔量的4倍、晶化温度为60℃、溶液酸度为0.016 mol/L、硅源预水解时间为6 h、硅钛比为40时合成的Ti-EPMO在环己酮氨肟化反应中具有最优的催化性能。最后,分别以BTEE和TEOS为硅源合成了钛掺杂乙基桥联的有机无机杂化介孔(Ti-HPMO)分子筛,并以环己酮氨肟化作为探针反应考察了其催化氧化性能。结果表明骨架内有乙基桥联(-C-Si-O-)的Ti-HPMO具有规整的六方介孔孔道和较高的疏水性,较以TEOS为硅源得到的无机介孔分子筛在反应中呈现较高的肟选择性。进一步研究了模板剂移除和酸处理对Ti-HPMO中钛物种存在形式的影响并与其环己酮氨肟化的催化性能相关联,认为有机杂化的介孔分子筛中的四配位钛和非骨架的六配位钛均为环己酮氨肟化反应活性中心。
[Abstract]:Titanium doped organic group bridged mesoporous molecular sieves Ti-PMOs are a new kind of mesoporous materials, which not only have the advantages of homogeneous pore size, high specific surface area and pore volume of conventional inorganic mesoporous molecular sieves. Moreover, the organic groups are uniformly distributed in the mesoporous framework, which can protect the Si-O-Si bond from hydrolysis, so it has excellent hydrothermal stability and hydrophobicity. Therefore, Ti-PMO has a potential application prospect in some macromolecular liquid phase oxidation reactions. Although it is generally believed that the isolated framework tetracoordination titanium in titanium-containing molecular sieves is the active center of some selective oxidation reactions, the exact properties of the active sites remain controversial. In particular, there are more and more reports that tetra-coordinated titanium species in the skeleton are not the only active centers. In this paper, commercial TS-1 was used as catalyst to optimize the reaction conditions of cyclohexanone ammoximation, which provided the basis for the evaluation of mesoporous molecular sieves. In order to match the concentration of H _ S _ 2O _ 2 and NH3 in the reaction process and keep the reaction in alkaline condition, ammonia water was fed in batch and equal proportion. After optimization, the molar ratio of cyclohexanone, ammonia and hydrogen peroxide is 1: 2.5: 1. 25. Secondly, Ti-EPMO-organic hybrid mesoporous molecular sieve with good hydrothermal stability was synthesized by using TiCl3 as titanium source. The addition of inorganic salts, crystallization temperature and acidity of the solution were systematically investigated. The effects of the pre-hydrolysis time of silicon source and the ratio of silicon to titanium on the physical and chemical properties of molecular sieve were studied. The catalytic properties of the molecular sieve were evaluated with cyclohexanone ammoximation as the probe reaction. The results show that inorganic salt is an important factor in the formation of two-dimensional hexagonal mesoporous structure of Ti-EPMO, and the effects of temperature, acidity and ratio of Si to Ti on the content of titanium and the coordination form of titanium in molecular sieve are greater, when the amount of inorganic salt added is 4 times of the molar amount of Si. When the crystallization temperature is 60 鈩，

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