多级孔MFI分子筛的精准制备及其MTA反应性能研究

Aromatics serve as the significant chemical raw materials, thus it is of great significance to develop effective and stable methanol-to-aromatics (MTA) catalysts for decreasing the dependence on the petroleum resources and guaranteeing the energy safety. Zinc modified ZSM-5 shows a high aromatics selectivity during the MTA reaction, however, the intrinsic microporous structure of ZSM-5 facilitates coke deposition reactions, finally leading to a low stability. Alkaline treatment can enhance the catalytic stability of MTA catalysts, most of the studies focus on the variation of porosity and diffusion performance after treatment, however, there is still a lack of systematic and in-depth understanding on the combining regulation of the acid amount, acid distribution, hierarchical structure and zinc distribution through the alkaline treatment of ZSM-5. Aiming at this problem, this project will synthesize a series of ZSM-5 samples, then the finely modulated alkaline treatment processes will be performed on those samples. The influence mechanism and essential inducement of alkaline treatment on the acid amount will be disclosed by combining instrumental characterizations and DFT calculations. Besides, hierarchical ZSM-5 with different acid distributions on the outer surface or inter part will be prepared by alkaline treatment, and also the regulation of the acid sites in the mesopores or the micropores will be realized. Based on those contributions, the relationship between acid distribution, hierarchical structure and zinc distribution-aromatization capability will be clarified. Finally, the combining regulation of acid amount, acid distribution, hierarchical structure and zinc distribution will be achieved through finely modulated alkaline treatment method. This project will provide a new method for regulating acidity and preparing superior MTA catalysts.

芳烃是重要的基础化工原料，开发高效、稳定的甲醇制芳烃（MTA）催化剂对降低石油依赖度和保障能源安全具有重要战略意义。MTA反应的催化剂多为锌改性ZSM-5分子筛，其芳烃选择性较高，但容易快速积炭失活。碱处理法可提高催化稳定性，但目前的研究多集中于对ZSM-5孔道结构和扩散性能的影响，而对于碱处理法协同调变ZSM-5的酸量、酸分布、多级孔结构和锌分布，一直缺乏系统而深入的认识。针对该问题，本项目设计合成一系列ZSM-5分子筛，通过精细调控碱处理过程，并结合表征和理论计算，揭示碱处理对ZSM-5酸量的影响机制和本质原因，同时实现酸性位点在多级孔ZSM-5内外表面或介微孔中的可控分布，并阐明酸分布、多级孔结构与锌分布-芳构化性能之间的关系。最终，通过精细调控碱处理过程实现对ZSM-5酸量、酸分布、孔结构和锌分布的协同调变。本项目将对分子筛酸性可控调变和高性能MTA催化剂制备提供指导。

碱处理法构筑多级孔结构是优化分子筛扩散性能的关键手段，但处理过程中酸量变化制约其在催化反应中性能提升，目前碱处理对酸量影响机制仍缺乏研究。本项目设计合成铝分布和单胞内铝含量不同的ZSM-5分子筛并对其进行碱处理，通过多种先进表征手段分析其脱硅过程，首次发现处理过程中铝迁移是影响其酸量变化的关键；更重要的是揭示了晶体内富硅区域大小与铝迁移程度之间的关联关系，最终实现碱处理对酸量的可控调变；通过优化碱处理法精准匹配脱硅和铝迁移过程，进而实现对分子筛酸量和孔结构的耦合调控，得到的最优催化剂在1,3,5-三异丙基苯和甲醇转化反应中表现出优异的性能。此外，以铝位点和模板剂区域分布的分子筛样品为材料基础，通过优化碱处理方法实现酸性位点、Zn物种在多级孔分子筛内外表面以及介微孔中的选择性分布。基于上述工作的开展，发展了分子筛酸性可控调变新方法，一步法实现对分子筛酸量和孔结构的协同优化。设计制备的多级孔ZSM-5分子筛材料在高湿条件下多组分VOCs吸附过程中呈现出优异性能，目前已完成该材料放大合成，正在推动其工业应用。