酸功能化木质素基有序介孔碳制备及其催化果糖脱水反应机理

Mesoporous solid acid has been an important catalyst to achieve efficient dehydration of fructose to hydroxymethylfurfural owing to its outstanding catalytic activity and stability. Lignin is a good carbon precursor, and its high-value utilization in preparation of carbon-based solid acid has become the research hotspot. Aiming to the problems of low surface area and poor stability of lignin-derived solid acids prepared via traditional pyrolysis/hydrothermal carbonization followed by sulfonation, and based on being rich in phenolic hydroxyl group of lignin structure as well as excellent reusability of ordered mesoporous carbon, lignin-derived ordered mesoporous solid acid prepared by using lignin degradation products liquefied in phenol and formaldehyde as carbon source is creatively presented. In this work, the methods of thermochemistry liquefaction in phenol and evaporation induced self-assembly are adopted, respectively. The effects of liquefied condition in phenol, template agent, mineral acid, carbonization temperature and sulfonation method on the properties of catalyst including porous structure, surface groups, distribution and strength of acid sites will be investigated, respectively. Combined with structure characterizations of mesoporous carbon and solid acid, surface adsorption as well as performance evaluation for fructose dehydration reaction, the catalytic reaction mechanism will be explored and the catalyst structure-activity regulatory mechanism will be clarified. Finally, lignin-derived ordered mesoporous solid acid with good performance will be obtained. This study can also provide theoretical support for the efficient preparation of biomass-based ordered mesoporous carbon as well as the application in biomass transformation.

介孔固体酸兼具突出催化活性和优异重复利用性，已成为实现果糖脱水制5-羟甲基糠醛的重要催化剂。木质素作为一种优质碳源，用于制备碳基固体酸是其高值化利用的重要研究方向。针对传统热解/水热碳化磺化法所制备木质素基固体酸存在比表面积低、重复利用性差的问题，本项目创新性地提出以木质素酚化液化降解产物/甲醛体系为碳源制备木质素基有序介孔固体酸，旨在充分利用木质素富含酚羟基的结构特征，并发挥有序介孔碳在重复利用性能上的显著优势。采用热化学酚化法和溶剂挥发诱导自组装法，分别考察酚化条件、模板剂、无机酸、碳化温度以及磺化方法对催化剂孔道结构、表面基团和酸性位点分布及强度的影响。结合介孔碳及固体酸结构表征、表面吸附性和果糖脱水反应性能评价，探索催化反应机理，寻求构效调控机制和规律，获得催化性能优异的木质素基有序介孔固体酸。本项目的完成，可为生物质基有序介孔碳材料的高效制备及在生物质转化中的应用提供理论支撑。

介孔固体酸兼具突出催化活性和优异重复利用性，已成为实现果糖脱水制5-羟甲基糠醛（5-HMF）的重要催化剂。木质素作为一种天然可再生的优质碳源，用于制备碳基固体酸是其高值化利用的重要研究方向，也在一定程度上减少了对石油资源的依赖性。针对传统热解/水热碳化磺化法所制备木质素基固体酸存在比表面积低、重复利用性差的问题，本项目开展了木质素基有序介孔碳（LDMC）及磺酸功能化木质素基有序介孔碳（LDMC-SO3H）的制备工艺和LDMC-SO3H在果糖脱水制5-HMF工艺中对反应体系的吸附性能及催化反应性能、机理的研究工作。结果表明，酚化预处理可以得到高酚羟基含量以及低分子量和多分散性指数的改性木质素。通过软模板法，以优化的酚化木质素为碳源，利用溶剂挥发诱导自组装技术制备出具有二维六方孔道的LDMC。经浓硫酸磺化后，所得LDMC-SO3H在大量引入磺酸基团（0.65 mmol/g）的同时，仍能保有较大比表面积（262 m2/g）和有序介孔孔道结构。以优化的LDMC-SO3H为催化剂，在反应温度140 ℃、反应时间2 h、果糖浓度100 g/L、催化剂负载量10 wt%、反应溶剂为二甲基亚砜的优化条件下，果糖转化率、5-HMF产率和反应选择性分别为100%、98%和98%。LDMC-SO3H经9次循环使用后，5-HMF产率仍高达83%，显示出优异的催化活性及稳定性。LDMC-SO3H的加入显著降低了果糖脱水反应活化能，促进果糖高效转化。此外，LDMC-SO3H对果糖的吸附符合多孔催化剂扩散控制的结果，且其对果糖的吸附量很大（691 mg/g），而基本不吸附5-HMF，这种吸附性能的显著差异能够在促进果糖经酸催化脱水高产5-HMF的同时，避免5-HMF再经酸催化水合生成副产物，从而显著提高反应选择性。本项目的完成为生物质基有序介孔碳材料的高效制备及在生物质转化中的应用提供理论支撑。