沸石分子筛催化剂表面多级微纳结构的仿生构建及其抗积碳性能强化研究

Although zeolite catalysts hold a profound market value, their design and engineering to reduce coking and expand catalyst lifetime remains to be a challenge. Different viable methods have been proposed, which indeed reduce coking, but demonstrate limited industrial application due to multiple unfavored factors such as significant surface barrier, demanding synthesis protocols and/or restricted implementation on different types of zeolites. In this proposal, we plan to mimic the unique surface structure of the stigma of certain flowers to construct similar hierarchical micro/nano-structures on several industrial-relevant zeolite crystals, with the help of zeolite growth modifiers. These novel zeolites will then be tested as catalysts in their representative petrochemical reactions, to examine the lifetime, activity and selectivity. We propose that the lifetime and coking resistance of the novel zeolite catalysts will be drastically improved with repetitive optimization of the morphology, number density and thickness of the biomimetic hierarchical micro/nano-structures. The proposed micro/nano-structures possess shorter diffusion pathlength and may improve internal/external diffusion via different mechanisms, thus contributing to the reduction of coking. They may also help improve the loading of metal particles and relieve their aggregation at high temperatures. In addition, the novel catalysts maintain the advantages of unmodified regular zeolite crystals including low surface barrier, well-developed synthesis procedure and industrial application. To sum up, the success of the proposed research project will generate an academically and industrially preferred zeolite design approach for the debottlenecking of coking problem, set a foundation for further diffusion and mechanism studies, while inspires the surface design of other heterogeneous catalysts.

沸石分子筛催化剂在创造巨大价值的同时，面临容易积碳失活的瓶颈问题。当前解决此问题的不同方案虽确实缓解了积碳现象，但受限于表面壁垒严重、技术难度大、适用范围小等诸多缺陷，难以直接应用于成熟工业流程。本项目拟模仿花朵柱头的表面结构，借助沸石修饰剂，在广泛使用的数种沸石晶种上仿生构建多级微纳结构，制备新型催化剂，并在代表性反应中进行应用测试。在此基础上，对该表面微纳结构的属性进行高精度优化，最终达到有效强化新型沸石催化剂抗积碳性能、大幅提高其寿命的目标。微纳结构的存在有望缩短催化剂的扩散路径，促进内外扩散，减缓积碳形成，还可提升金属活性中心负载量、限制其热团聚。同时，本催化剂也能保留原晶种表面壁垒小、制备技术和工业应用成熟的优势。本项目的完成，将为沸石催化剂积碳这一瓶颈问题的突破提供有竞争力和产业价值的新思路，为更深入的传质与反应的机理研究奠定基础，也将给其他异相催化剂的表面设计提供借鉴和参考。

为切实有效的解决催化剂活性不足且容易积碳失活的瓶颈问题，本项目模仿花朵柱头的表面结构，借助晶体修饰剂在材料表面构筑了形貌、密度等属性可调控的仿生多级微纳结构。实验发现微纳结构的存在促进了载体与金属纳米颗粒间的相互作用强度，同时对反应物分子体现出富集效果，因而将生物质加氢转化反应的转化率和选择性提升了4~5倍。由于微纳结构对尺寸相近的分子选择性吸附作用更强，因此具有一定的分子识别效果，但对CO2等小分子的捕获能力有限。针对此问题，项目执行中将微纳结构的概念进行了拓展，针对小分子反应物开发了具有界面耦合特性的绿色可实用催化剂，并实现了界面耦合这一微观概念与宏观微纳结构的协同作用，成功的提升了催化剂对小分子的富集效果，取得了有竞争优势的CO2还原活性与选择性。为进一步调控微纳结构属性，构筑适合不同尺径分子的新型催化剂，我们从基础科学出发，探讨了修饰剂与催化剂晶体的相互作用模式，发现二者的相互作用受动力学控制，而非传统认为的热力学过程。同时，也进一步丰富了修饰剂的内涵，开发了基于等离子技术的新型绿色修饰剂。还首次将修饰剂应用于磷烯材料的溶剂热合成，获得了具有超高催化活性和稳定性的新材料。本项目的执行过程统筹兼顾了原定计划和实际情况，既超额完成了预期目标，又对上下游相关概念进行了深化和拓展，从基础科学和实际应用两方面取得了具有一定价值的科研成果，同时对跨学科、跨地区交流和人才培养也起到了一定的推动作用。