生物质碱性纳米片断键-酸性微孔择形协同催化热解制取单苯环类化合物的基础研究

Biomass contains plenty of benzene groups and can be catalytically pyrolyzed for high-valued chemicals with one benzen-ring (phenols, alcohols with benzen-ring, aromatics). In most studies, single microporous catalysts are used for targeted products with high selectivity by micropore shape selecting. However, biomass pyrolysis produce a lot of large molecules which can not enter micropores, and will polymerize on the external surface of catalysts and finally lead to coking and deactivation. In this project, we propose a new method about a dual acid-alkali catalysis in which large molecues are converted into stable small molecules by bond breaking and primary deoxygenating with alkali catalyts followed by acid catalysts for shape-selective conversion. We propose the systhesis method of nanosheet bond-breaking alkali catalyst by intercalating self-assembly which is beneficial for large molecules diffusion, and the stablization of oxygen-rich group can weaken pore blocking. On one hand, in-situ infrared spectroscopy is introduced to record evolution rules of functional groups online. Catalytic experiments with isotopic tracing and quantum chemistry calculation are also combined. Then mechanism of alkaline bond breaking, primary deoxygenation and acid shape-selective catalysts are revealed. On the other hand, we will study the structure activity relationship of catalysts. The method of controlling the growing characteristics of alkali nanosheet crystals, pore structure and thickness of nanosheet, and modifying by atomic layer deposition will also be obtained. Synergy mechanism of alkali bond breaking and acid shape-selective catalysis will be revealed. By this study, it will provide a new pathway for chemicals with single-benzene chemicals producting efficiently from biomass.

生物质中含有大量苯环结构，对其催化热解可以直接获得高附加值单苯环类化学品（酚、苯基醇、芳烃等）。目前大多研究采用单一微孔催化剂，需要利用微孔择形作用制取目标产品。但生物质热解产生大量大分子物质，它们不仅不能进入微孔被转化，而且还会在催化剂表面聚合引起结焦失活。基于此，本项目提出采用碱性催化剂将大分子断键、初步脱氧为较稳定小分子，然后采用酸性催化剂择形转化的酸碱复合催化新思路。提出采用插层自组装方法合成纳米片状碱性断键催化剂，片状结构有利于大分子扩散，固定富氧基团后不易造成孔道堵塞失活。引入原位红外在线监测官能团演变规律，结合同位素示踪催化实验和量化计算，揭示碱性断键和初步脱氧机理以及酸性择形催化机制；研究催化剂构效关系，获得调控碱性纳米片晶体长大、孔隙结构、纳米片厚度和原子层沉积颗粒尺寸的方法，揭示碱性断键-酸性择形催化协同作用机制。通过研究，为生物质高效制备单苯环类化学品提供一条新途径。

生物质催化热解能够将生物质一步转化为高品质航油重要组分，但由于生物质热解组分中含有大量无法进入催化剂微孔的大分子，造成了催化剂快速结焦失活和烃类目标产物产率低等两大瓶颈问题。基于此，本项目提出采用断键催化剂首先对大分子进行断键生成小分子，然后再进入微孔择形分子筛催化剂孔道进行择形催化的新思路，项目按照任务书的要求认真展开工作，取得如下重要成果：（1）原料处理层面，揭示了溶剂预处理对生物质微观结构和热解过程的影响机制，创新性地提出芬顿预处理弱化连接键，有效增加轻质生物油产率及脱氧率的方法；（2）热解大分子断键方面，率先提出以氢氧化物纳米粒子为前驱体，设计了稳定性强、抗结焦的层状水滑石碱性断键催化剂，通过添加活性组元和骨架三价Al，获得不同金属位及匹配对断键产物产率和选择性的调控规律；（3）热解小分子择形催化方面，揭示了催化剂外表面酸位点的作用机理，设计了HZSM-5@silicalite-1复合沸石催化剂，显著提升了择形脱氧和抗积碳性能，相较原HZSM-5催化剂，壳层覆盖度为78.8%的CS2样品作用下烯烃+单环芳烃总碳产率提高了9.6%，催化剂积炭和多环芳烃碳产率分别降低了22.1%和19.2%；（4）热解大分子断键产物与择形催化剂孔道尺寸匹配规律方面，发现择形催化剂HZSM-5在高温催化过程中孔道尺寸大于常温下物理尺寸，提出“有效直径”的概念，通过量子化学计算和萘烷基化实验确定了最佳有效直径介于7.520和7.961 Å之间，实现了热解断键产物与择形催化剂孔道尺寸关系的定量描述，获得了热解断键与择形催化脱氧之间的耦合关系；（5）生物质断键与择形协同方面，采用水滑石、木质素炭和USY等断键催化剂，研究了原位与非原位耦合方式下协同催化产物分布特性，揭示了各断键催化剂与微孔择形催化剂协同作用机理，在最优工况下，总芳烃收率与单一ZSM-5相比提高2.52倍；（6）生物质与富氢原料共催化热解提高目标产物降低结焦率方面，从原料层次上解决生物质贫氢问题，获得了共催化机理，采用共催化热解实现了催化剂结焦最小化，目标产物收率提高7.7。以上研究为生物质高效转化为先进液体燃料奠定了理论基础，具有重要的科学意义。