核壳空心MFI封装镍催化剂构筑及C5/C6烯烃叠合制备航空煤油反应研究

Due to the restriction of environmental regulations, it is practical significance to study the rational utilization of C5/C6 olefins. C5/C6 olefins are promising materials for the synthesis of high-quality aviation fuel through oligomerization. Key problems with oligomerization catalysts are their low selectivity, lack of stability and easy deactivation. Hollow ZSM-5 zeolites used in this project could greatly reduce the diffusion limitations. It is easy to study the mechanism of oligomerization in hollow ZSM-5 with controllable structure. We will show the relocation of silicon and aluminum in the dissolution–recrystallization process for synthesizing hollow ZSM-5. The distribution of the aluminum, the acid density and the distribution of acid centers on the surfaces and inner surfaces of the hollow ZSM-5 could be finely tuned. The influence law of acid properties on oligomerization would be obtained in this study. In this project, hollow MFI zeolites with shells encapsulating metal oxide are designed to generate high efficient catalyst with the coordination of metal center and acid center. Through precisely control of the hollow and shell structure in MFI, targeted encapsulating metal particles in the hollow MFI crystals has become possible. Moreover, the distance between the metal catalytic center and the acid center could be modulated. Then, the two types of catalytic centers are designed to realize the effective separation and cooperation with each other in order to achieve deep understanding of reaction mechanism and carbon deposition mechanism. The synergistic relationship between the metal center with different size and the acid sites of hollow ZSM-5 zeolite with different acid distribution and acid density would be studied. The project could provide theoretical basis for the development of highly effective catalysts in oligomerization and establish a basis for industrial applications.

受制于环保法规等的限制，将C5/C6烯烃合理转化利用具重要研究意义。C5/C6烯烃通过叠合反应可成为制备高品质航空燃油的理想原料。本项目针对烯烃叠合催化剂选择性低、稳定性差和易于失活的难题。以结构可控的空心ZSM-5分子筛为基质，促进扩散性能，并便于研究叠合机理。精细调变ZSM-5分子筛的二次晶化过程、内外表面酸性质的形成机制，建立调控酸中心分布和酸密度的方法，揭示酸中心对叠合反应的影响规律。以核壳空心MFI封装镍氧化物为结构设计基础，通过精准调控MFI空心层和壳层结构，实现定向封装金属，调控金属催化中心和空心ZSM-5分子筛酸性中心有效位点距离，以实现两类催化中心空间有效隔离和效用互相配合，深入认识反应机理及积炭控制。研究金属中心尺寸与具有不同酸密度和酸中心分布的空心ZSM-5分子筛酸中心的协同关系，提升两者协同作用，为高效叠合催化剂的设计提供科学依据，推动其工业化应用。

烯烃叠合反应是重要的低碳烯烃转化过程，将C5-C6资源叠合为C9-C16资源，以用于生产高品质的航空燃油具有良好的应用前景和实用价值。但其关键之处仍是找到合理的催化剂，减少催化剂失活，提高催化剂活性和稳定性。本课题一方面对微孔ZSM-5、核壳结构ZSM-5及多级孔ZSM-5分子筛微观结构和酸性及叠合性能进行了研究，建立构效关系，识别调控的关键因素；另一方面考察了金属在分子筛基质中存在状态及金属Ni与分子筛本体相互协同作用机制对烯烃叠合反应性能的影响规律。探索了锚定Ni物和稳定催化剂的可行方法。具体研究内容分为三部分，在前期探索核壳空心ZSM-5分子筛催化1-己烯叠合反应的活性较低的基础上，第一部分重点探讨了微孔ZSM-5酸性质对1-己烯烯烃叠合反应的影响规律。第二部分，拓展了核壳ZSM-5样品的合成手段，分别通过水热法和蒸汽相两种方法得到了表面为ZSM-5小晶粒，核层为ZSM-5晶体的核壳ZSM-5分子筛，结果表明具有小晶粒的核壳ZSM-5分子筛可以有效促进大分子参与的催化裂解反应，但对于1-己烯烯烃叠合的性能提升有限。以此启发，通过无模板法合成了保留酸量的多级孔ZSM-5分子筛，并在1-己烯烯烃叠合反应中实现了初始活性和稳定性的显著提升（初始活性高于商业ZSM-5分子筛数倍）。并采用平均空时产率、各馏分段比例详细对催化剂结构和催化性能进行了关联，完善了催化剂活性评价和反应机理研究工作。第三部分，系统性研究了金属Ni在ZSM-5分子筛上的分布状态对叠合反应的影响。对离子交换态的Ni和分子筛合成进行了进一步优化，研究了Ni和分子筛的协同作用对1-己烯烯烃叠合反应性能的影响。本项目有助于认识低碳烯烃叠合过程，并为高效叠合催化剂设计与开发提供了理论指导。