基于氢转移策略的生物质/甲烷耦合催化热解定向制取单环芳烃基础研究

Catalytic pyrolysis of biomass and methane are the most promising routes for monocyclic aromatic production (benzene、toluene and xylenes）from non-petroleum resources. The critical problems facing catalytic pyrolysis of biomass are low yield of monocyclic aromatics and rapid deactivation of catalyst caused by severe coking. And there is a contradiction between the severe coking during methane activation at high temperature and low efficiency of methane activation at low temperature. In order to address these challenges, catalytic pyrolysis of biomass coupling with methane activation is proposed. During the coupling pyrolysis, the hydrogen transfer reactions between methane and olefins from biomass catalytic pyrolysis can achieve for the low-temperature activation of methane, and the hydrogen releasing from methane activation can simultaneously inhibit the dehydrogenation reactions of high active intermediates to form fusing-aromatics and coke. Transition metals confined in ZSM-5/Y core-shell zeolite are constructed for orientated synthesis of monocyclic aromatics according to the mechanism of coupling pyrolysis. The transition metals and ZSM-5 zeolites are responsible for the aromatization of biomass and methane. The Y zeolites are responsible for the in-situ cracking of fusing-aromatics. The effects of preparation methods and transition metal precursors of multifunctional catalysts on their pore structure, acidity natures and the size，exposed crystal surface，location and coordination structure of transition metal ions, and their subsequent impacts on reaction paths and product distribution from coupling pyrolysis, are systematically analyzed. The relationships between the structure of multifunctional catalysts and their catalytic performances are established and discussed. These studies can provide theoretical basis and technical support for effective conversion of biomass and methane towards monocyclic aromatic production.

生物质和甲烷是非石油路线制取芳烃的重要途径。针对生物质单独催化热解存在单环芳烃收率低和催化剂易积碳失活等问题，另外考虑到甲烷单独芳构化存在着高温积碳严重和低温活化困难的矛盾，本申请提出生物质催化热解耦合甲烷低温活化的反应体系，通过生物质催化热解原位产生的烯烃和甲烷的氢转移反应实现甲烷低温活化；同时甲烷释氢抑制生物质热解活性中间物种脱氢生成稠环芳烃和积碳。然后依据该机制指导构筑ZSM-5/Y壳核分子筛限域的纳米过渡金属氧化物催化剂，其中过渡金属氧化物和ZSM-5协同负责生物质和甲烷的芳构化，Y分子筛负责临氢条件下稠环芳烃的催化裂化，进而实现定向制取单环芳烃。系统考察核壳分子筛的构筑方法及过渡金属物种选择与其多级孔道结构、表面酸性、过渡金属离子的尺寸、晶面曝露、落位及配位结构对耦合热解反应历程和产物分布的调控规律。建立催化剂构效关系，为生物质/甲烷高效制取单环芳烃提供理论指导和技术支撑。

生物质和甲烷是非石油路线制取单环芳烃的重要途径。针对乏氢生物质单独催化热解存在单环芳烃收率低和催化剂易积碳失活等关键问题，另外考虑到富氢甲烷单独芳构化存在着高温积碳严重和低温活化困难的矛盾，本申请提出生物质催化热解耦合甲烷低温活化制取单环芳烃新工艺。成功合成了一系列包含W、Mo、Ti、Zr或Al的新型纳米复合物金属氧化物固体酸催化剂并成功应用于生物质催化热解定向制取芳烃和呋喃类化合物，机理研究证明WO3-TiO2-Al2O3（WTA）可以通过木质素衍生酚类的脱甲氧基及脱水反应来生成芳烃，WTA也可通过选择性断裂综纤维素中的C-O键经脱水反应生成呋喃类化合物。呋喃类化合物进一步和甲烷耦合催化热解用于制取芳烃。合成了一系列机械混合HZSM-5/HY复合分子筛、HZSM-5@HY及HY@HZSM-5壳核分子筛和金属负载分子筛催化剂，并应用于呋喃类化合物（2-甲基呋喃，2-MF）催化热解及其与甲烷的耦合催化热解。研究发现与单独催化热解相比，耦合热解将BTEX碳收率提高了24.2%，各种催化剂中MoZn/HZSM-5对甲烷活化的能力最强。首次发现了2-MF芳构化的关键中间体苯并呋喃类和环戊烯酮类化合物，提出2-MF芳构化的两条主要反应途径：2-MF自身发生Diels-Alder反应生成苯并呋喃类化合物，苯并呋喃类化合物再经过脱羰基反应生成芳烃和CO；2-MF经催化也会生成环戊烯酮类化合物，环戊烯酮类化合物经异构化反应及脱水反应生成芳烃。耦合催化热解中，甲烷活化生成的甲基自由基有利于2-MF及其中间体的转甲基化反应及其随后的芳构化反应，进而有效提高了芳烃收率并降低了积碳生成。发现分子筛催化剂的弱酸量及孔径与积碳的生成相关，分子筛较高的弱酸酸量和较高的平均孔径有利于降低催化剂积碳。项目共发表标注论文22篇（其中包括SCI论文21篇）并申请发明专利3项，项目的顺利实施为生物质/甲烷耦合热解制取单环芳烃提供了理论基础和技术支撑，对于维护国家能源安全、实现双碳战略目标和乡村振兴战略目标具有重要意义，应用前景广阔。