多功能MOF催化转化纤维素制乳酸/乳酸酯的构效机制

At present, fossil products (such as polyethylene plastic, etc.) had resulted in serious environmental pollution. The conversion of renewable resources (such as cellulose, Cn) to platform compounds (such as lactic acid/lactate), and then the synthesis of green materials (such as polylactic acid, etc.) will be one of the fundamental and effective ways to solve this problem. However, the production of lactic acid by fermentation involves the problems of food competition in raw materials, difficulty in controlling the acidity of the fermentation broth and low yield, etc. The selectivity of traditional chemical catalysis is low, while its energy consumption is very high. In view of these questions, this project will firstly clarify the catalytic mechanism of Lewis acids (L acids) on the isomerization of C6-aldoketoses (glucose→fructose) and the cleavage of C6-ketose's C-C bonds (C6-ketose→ glyceraldehyde and dihydroxyacetone), providing the theoretical foundation for the construction of L acid-based metal-organic framework (MOF) catalyst with high selectivity. Moreover, this project will focus on revealing the synergetic mechanism between binding domain and B acid for hydrolyzing Cn to C6-aldose and analyzing the inhibition effect of carrier channels on the mass transfer efficiency of catalytic intermediates. Finally, this project will construct a multifunctional MOF catalyst with the structure of hierarchical pore, L acid and biomimetic B acid and uncover its structure-activity mechanism, which will be beneficial to realize efficiently heterogeneous conversion of Cn to lactic acid/lactate. The research of this project will provide theoretical and technical support for alleviating the crisis of energy and environment in our country.

目前，化石制品（如聚乙烯塑料等）已对环境产生严重污染，将可再生资源（如纤维素，Cn）转化为平台化合物（如乳酸/乳酸酯）、进而合成绿色材料（如聚乳酸等）将是解决此问题的根本有效途径之一。然而，发酵法生产乳酸涉及原料存在粮食竞争、发酵液酸度不易调控、产率低等问题；传统化学催化选择性低、能耗高。据此，本项目首先阐明路易斯酸（L酸）对碳六（C6）醛酮糖异构（葡萄糖→果糖）及C6-酮糖C-C键断裂（C6-酮糖→甘油醛和二羟基丙酮）的催化机制，为构建高选择性L酸金属-有机骨架（MOF）催化剂奠定理论基础；其次，揭示结合域对质子酸（B酸）催化Cn水解为C6-醛糖的协同促进机制；同时，分析载体孔道对催化中间产物传质效率的抑制作用；最终，构建具有多级孔、L酸和仿酶型B酸结构的多功能MOF催化剂，揭示其构效机制，实现Cn到乳酸/乳酸酯的高效非均相催化转化。项目研究将为缓解我国能源和环境危机提供理论和技术支持。

高效非酶催化纤维素转化为乳酸不仅可促进绿色材料和功能化学品产业的发展，而且有利于缓解能源和环境问题。本项目主要研究多功能金属有机骨架(MOFs) 材料催化纤维素转化为乳酸的构效机制。首先，基于磺化后处理和有机配体苯环侧链修饰，将Brønsted酸（如-SO3H）和结合域（如-OH、-Cl、-Br或-NH2等官能团）引入MOF材料；其次，以In、Al或Zr等金属为Lewis酸、SO3H为Brønsted酸，解析Lewis酸所介导C6醛/酮糖异构、C6酮糖逆羟醛和C3糖（1,3-二羟基丙酮与甘油醛）氢转移等主反应路径、以及Brønsted酸引发单糖（如葡萄糖）的脱水、逆羟醛、羟醛缩合以及脱羧等副反应，进而产生呋喃化合物（如羟甲基糠醛等）、以及C2‒C4小分子（乙醇酸、甘油酸、2-羟基丁酸和乙酰丙酸等）等副产物；同时，采用电镜和紫外漫反射等分析仪器表征所合成多功能MOF材料的结构，据此开发酸后处理等缺陷手段来构建高密度及活性的L酸，调控MOF材料中L酸和B酸比例；最终，开发廉价过渡金属（如Ni2+和Zn2+等）作为Lewis酸，使碳水化合物衍生单糖（果糖和葡萄糖）转化为乳酸的得率达到50%左右。目前，本项目已在Angew等国内外期刊发表论文7篇，申请中国发明专利2件、其中1件已授权，5名研究生参与该项目研究。