二维MFI沸石等级孔道精准调控及芳香烃傅克苄基化反应性能探究

2D (two dimensional) MFI zeolites have drawn great concerns in Friedel-Crafts benzylation of aromatics with benzyl alcohol owing to its high external surface and exposed active sites. The major challenge for benzylation of aromatics with benzyl alcohol is the limitation of tailoring the selectivity of target monobenzylated aromatics, because the self-condensation of benzyl alcohol and polybenzylation of monobenzylated aromatics decrease the selectivity of monobenzylated aromatics as the side reactions. To overcome the above barrier, we propose a novel of approach to investigate the effect of hierarchical structure of 2D MFI zeolites on selectivity of monobenzylated aromatics, which is performed based on the catalytic ability of Brønsted acid sites and Lewis acid sites located on the surface of zeolites with self-condensation and polybenzylation reactions, respectively. In addition, the diffusion rate of hierarchically structured 2D MFI zeolites is also a decisive factor to determine the reaction pathway of benzylation of aromatics. The proposed work will focus on (a) fundamentally understanding of the structure-performance relationships between hierarchical structure of 2D MFI zeolites with synergistic effect of Brønsted/Lewis acid sites and diffusion rate; (b) mechanistic achievement of a novel of approach to effectively tuning the hierarchical structure of 2D MFI zeolites. Developing a highly efficient reaction process for benzylation of aromatics based on the control of hierarchical structure of 2D MFI zeolites. The developed proposal opens a door for generation of a green benzylation of aromatics with benzyl alcohol, and thus this is vital in application.

针对二维MFI沸石应用于芳香烃傅克苄基化时，由于同时存在苄醇的自醚化和二芳基甲烷的过烷基化副反应，导致难于调控单烷基化产物选择性的这一关键难题。本项目提出利用二维MFI沸石表面Brønsted酸和Lewis酸对自醚化和过烷基化反应催化能力的差异，以及二维MFI沸石等级孔道扩散速率对苄基化反应路径的控制，研究二维MFI沸石的等级孔道调控对芳香烃苄基化反应选择性的影响。本项目将从理论层面上分别研究二维MFI沸石等级孔道调控，对分子筛表面Brønsted酸/Lewis酸协同效应和分子筛微孔/介孔复合孔道扩散速率的影响规律。从技术层面上研制出一种精准调控二维MFI沸石等级孔道的新技术，建立基于二维MFI沸石等级孔道调控的低能耗高效芳香烃苄基化反应过程。该研究成果将为构建清洁低碳的芳香烃苄基化反应工艺提供理论和技术支持，具有重要科学意义和应用价值。

二维MFI分子筛因其超薄的厚度、开放的孔道、大量可接触的外表面活性位点以及独特的交叉孔道结构在大分子参与的三甲苯与苄醇苄基化反应中显示出了特殊优势，存在巨大的潜在应用价值。本项目按照申报书中的研究计划从二维MFI分子筛形貌、等级孔结构以及酸活性中心三方面入手，深入考察了二维MFI分子筛等级结构与酸中心调控对三甲苯与苄醇苄基化反应过程的影响规律。通过对Bola型表面活性剂的分子结构进行系统调变，精准控制其结构导向能力，成功制备出具有不同形貌的二维MFI分子筛。利用微孔模板剂四丙基氢氧化铵和双功能Bola型表面活性剂对分子筛结构导向能力的差异，通过优化双模板在分子筛合成溶胶/凝胶中的配比，构建具有稳定柱撑结构的有序二维MFI分子筛催化剂，解决了二维片层MFI分子筛多层有序结构在煅烧过程中易坍塌的难题。采用骨架掺氮的方法使氮原子部分取代分子筛骨架中的硅羟基和桥氧原子，对其酸中心进行系统调控。研究发现：Brønsted酸位点对苄醇的活化能力大于Lewis酸位点，提高分子筛骨架中的Brønsted酸与Lewis酸的比列，有利于苄醇的活化。通过系统控制二维MFI分子筛骨架中Brønsted酸与Lewis酸中心的相对浓度，对苄醇的质子化速率、自醚化速率、二苄醚水解速率以及与三甲苯烷基化速率进行系统调控，实现了对烷基化反应路径的定向控制，提高了2-苄基-1,3,5-三甲基苯产物的选择性(⁓70%)，建立了一种以二维MFI分子筛等级结构调控为核心的低能耗绿色芳烃苄基化技术。