木质素基环己烯合成中多功能催化剂构建和反应机理研究

The current synthetic routes of cyclohexene from petroleum-based material benzene has many key challenges and difficult problems to overcome, for example, thermodynamics and kinetics limitations, easily hydrogenation of cyclohexene to cyclohexane, low yield of cyclohexene. Therefore, we firstly propose the novel and efficient synthetic route of green cyclohexene using lignin-derived guaiacol from lignin catalytic and thermochemical processes. Firstly lignin-derived guaiacol is converted to phenol by selective cleavage of aryl C-O ether bonds on WP catalysts, then step to complete hydrogenation of phenol to cyclohexanol and cyclohexanol dehydration to cyclohexene on micro-mesoporous composite zeolites supported Ni. The selective cleavage of ether bonds can be promoted on WP catalysts by modification of acid/base oxides and active metals, indicating control factors and mechanism of selective bond cleavage. Micro-mesoporous composite acidic zeolites were prepared in situ by the hydrothermal technique with alkali-treated micro-zeolites as sources. The active Ni metal could be impregnated onto micro-mesoporous composite zeolites with double layer structure by the complexation-impregnation method. It is important to explore the law for forming double layer structure, the interaction between the nickel species and support surface for adjusting the particle size, surface diffusion mechanism using phenol as probe molecules in the micro-mesoporous composite molecular sieve. The research will attract wide attention for industrial development and application on the lignin-derived cyclohexene.

针对现有的石油基环己烯合成路线中环己烯产率偏低的难点，结合提升木质素高值化利用的关键点；提出利用愈创木酚高效合成环己烯的新合成路线：①愈创木酚在金属磷化物催化剂上选择性断键生成苯酚，②苯酚在镍基复合分子筛催化剂上耦合加氢和脱水反应生成环己烯。通过负载磷化钨催化剂的金属修饰和载体酸碱性调变促进愈创木酚的转化，控制醚键的选择性断键，研究选择性断键的控制因素，阐明构效关系与催化机理；通过以酸性微孔硅铝分子筛为硅铝源原位合成介孔分子筛使其具有双层结构的微介孔复合分子筛，利用络合浸渍方法在复合分子筛表面浸渍加氢活性组分金属镍，构建镍基复合分子筛组分微观结构，探索双层结构行成规律，研究金属镍和分子筛表面的相互作用对金属纳米粒子尺寸调节机制，分析苯酚等探针分子在微介孔复合分子筛中的扩散反应机理，为突破石油基环己烯合成路线和高效提取木质素基环己烯的工业开发和应用提供基础理论支撑。

目前环己烯工业生产中主要采取苯选择性加氢制备，原料依赖于石化资源，环己烯产率偏低。本课题提出利用来源于木质素降解单酚愈创木酚高效合成环己烯的新合成路线，以高选择高活性的催化剂制备和协同多功能的双层分子筛结构设计为切入点，完成了对愈创木酚母体分子进行定向剪裁，通过选择性断裂甲氧基生成苯酚或环己醇，耦合甲氧基选择性断裂、苯环加氢、环己醇脱水中间反应过程高效合成环己烯，实现木质素基环己烯的绿色合成工艺路线。具体研究结论如下：1. 发明了多元醇共浸渍负载型催化剂制备方法，强化了载体之间相互作用力，制备出高活性高分散的负载型催化剂，金属纳米粒径从48纳米降到3-5nm；表现出优良的苯环低温加氢活性，150℃愈创木酚转化率达到97.4%，55℃萘加氢转化率100%。2. 通过WP/MCM-41和Ni/MgO碱性双功能催化材料的高活性制备，实现调控选择性断裂醚键生成苯酚以及耦合苯环加氢反应促进高效生成环己醇，苯酚选择性达到100%，产率到73%；环己醇选择性达到98.3%，产率达到97.9%。3. 原位合成双层结构的复合分子筛，控制介孔孔径，实现加氢金属活性中心的孔道内外分布调控，介孔孔壁可以限制金属活性粒子的团聚，获得高温700℃工作均稳定的加氢催化剂；实现外层负载金属加氢和内层酸性位脱水功能的耦合反应功能。4. 通过耦合选择性断键和加氢脱氧两步反应，获得木质素基环己烯的合成效率，愈创木酚经苯酚中间产物可以获得24.3%环己烯产率，愈创木酚经环己醇中间产物可以大幅提高到环己烯产率至85.5%。5. 申请发明专利2件，已获得授权1件；已发表SCI论文4篇，接受中文核心1篇，正在审稿SCI论文2篇；参加国内外学术交流3次；培养青年科技骨干2人，培养研究生2人。目前主要存在的问题是木质素降解产物复杂，愈创木酚单一产物选择性约为5%，单酚产率偏低，如何高效定向降解木质素为单酚愈创木酚是关键的技术瓶颈。