磺酸功能化金属有机骨架材料封装磷钨酸复合催化剂的构建及其在环己烯甲酸酯化反应中的酸性调控

Cyclohexanol is the most important intermediate in the industry of caprolactam. Preparation of cyclohexanol from the indirect hydration of cyclohexene includes two steps: esterification of cyclohexene with formic acid and the subsequent hydrolyzation of ester. The indirect hydration process can overcome the defect of lower conversion of cyclohexene (<10%) and higher separate energy consumption caused by the direct hydration of cyclohexene, while esterification reaction is the key step to realize the indirect hydration process of cyclohexene. This project is aimed at conducting the composite catalyst formed by the sulfonic acid functionalized metal organic frameworks (MOFs) MIL-101(Cr) encapsulated tungstophosphoric heteropolyacid (HPW) and efficient implementation of the addition esterification of cyclohexene with formic acid by the modification effect of total acid amount, acid intensity and acid type of the composity catalyst. The effect of preparation conditions on the structure of the catalysts would be investigated and many means would be used to characterize the structure. The acid regulation effect for the esterification through the Lewis acid performance of metal node of MOFs, the Brønsted acid performance both of HPW and sulfonic acid functional groups would be mainly explored. Furthermore, we would pay attention to the reuse performance of this composite catalyst, especially identify the action mechanism of the chemical environment of MOFs modified by the sulfonic acid groups on restraining the loss of HPW. On the basis of the structure-activity relationship obtained from the above work, the reaction mechanism would be deduced. The research work can provide the theoretical guidance and technical support for the indirect hydration process of cyclohexene.

环己醇是己内酰胺工业的重要中间体，环己烯间接水合制备环己醇包括环己烯和甲酸的酯化以及酯水解两步反应，该工艺能有效克服环己烯直接水合工艺转化率低（＜10%），分离能耗大的缺陷，而酯化反应又是其中的关键步骤。本项目旨在构建磺酸功能化的金属有机骨架材料MIL-101(Cr)封装磷钨杂多酸复合催化剂，通过酸量、酸强度和酸类型的调变高效实现环己烯和甲酸的加成酯化反应。项目研究工作将通过各种对比样品的制备，考察制备条件对催化剂结构的影响，并采用多种手段进行详细的结构表征，重点探讨复合催化剂的总酸量以及金属有机骨架材料金属结点的Lewis酸性，磷钨酸和磺酸功能基团的Brønsted酸性对酸催化反应的调控作用，进一步考察催化剂的重复使用性能，明确磺酸功能化金属有机骨架材料的化学环境对抑制磷钨酸流失的作用机制。通过研究工作所获得的构效关系推导出反应机理，为环己烯间接水合工艺的实现提供理论指导和技术支持。

环己醇是己内酰胺工业的重要中间体，环己烯间接水合制备环己醇包括烯酸酯化以及酯水解两步反应，该工艺能有效克服环己烯直接水合工艺转化率低（＜10%），分离能耗大的问题，而酯化反应又是实现环己烯间接水合工艺的关键步骤。本项目首先通过构建金属有机骨架材料MIL-101(Cr)磺酸功能化后封装磷钨酸的复合催化剂，提高总酸量，高效实现环己烯和甲酸的加成酯化反应，在烯酸摩尔比1:3，催化剂用量5%，80℃下反应6h，环己烯转化率80.20%，甲酸环己酯的选择性为98.26%，证实了磷钨酸和磺酸基团的相互作用能抑制活性基团流失，有利于催化剂稳定性的提高；由于磺酸功能化MIL-101(Cr)存在非活性的磺酸基团，进而通过采用UiO-66为载体构建缺陷位的磺酸功能化UiO-66复合磷钨酸，缺陷位的构筑使UiO-66孔径分布扩大的同时，L酸和B酸量均得到很大的提升，催化剂用量0.5%的条件下可以提高环己烯的转化率为87.56%，甲酸环己酯的选择性为97.56%；但强极性的甲酸对MOF类催化剂的结构具有明显的破坏作用，因而采用极性弱不溶于水的环己甲酸替代甲酸进行酯化反应，构筑了缺陷位磺酸功能化UiO-66催化环己烯和环己甲酸的加成酯化体系，在烯酸摩尔比1:3，催化剂用量3%，150℃下反应8h，环己烯转化率50.54%，环己甲酸环己酯的选择性为86.56%，催化剂能够实现简单分离后重复使用，环己甲酸能保护MOF材料的结构稳定，催化剂的稳定性得到提升，而且该体系不会在后续水解过程产生大量的稀酸水溶液，可以有效降低分离能耗。本项目的研究为环己烯间接水合工艺的实现提供了理论指导和技术支持，对加成酯化反应体系的研究有借鉴意义。