Abstract:

Traditional microporous zeolites have uniform pore size, large specific surface area, strong acidity, ion exchange ability, and good shape selectivity. However, the traditional microporous zeolites suffer from high mass transfer and diffusion resistance, seriously reducing their performance. Hierarchical zeolites possess a multi-level pore structure, which can enhance the diffusion of large molecules, reduce coke accumulation, and improve catalysts' utilization, lifespan, and catalytic performance. Hierarchical zeolites are usually prepared by either "top-down" method or "bottom-up" strategy. This article mainly reviews the synthesis methods of hierarchical zeolites in recent years, and focuses on the "top-down" method with wide applications. The research on diffusion intensification for hierarchical zeolites in catalytic applications is comprehensively reviewed. It is pointed out that hierarchical zeolites have unique advantages in improving catalytic performance (such as activity, selectivity, catalytic stability). By introducing hierarchical pores in the framework of zeolites, the diffusion path within the zeolitic crystal is shortened, and the mass transfer diffusion restrictions are reduced. Hierarchical pore structure is also conducive to stabilize loaded metal active species, inhibiting their sintering in catalytic reactions and increasing the stability of supported zeolite catalysts. Finally, the advantage of hierarchical zeolites are discussed, i.e. strengthening internal diffusion performance and improving the utilization rate of internal centers in zeolites, and their preparation method and green production process are prospected.

Key words: hierarchical zeolite, mass transfer limitation, diffusion intensification, catalysis

摘要：

传统微孔分子筛具有均一孔径、较高比表面积、良好的择形选择性等优点，但受到传质扩散阻力限制，导致其性能严重降低。而等级孔分子筛具有多级孔道结构，可以强化大分子的扩散，减少焦炭堆积，从而改善催化剂利用率、寿命和催化性能。等级孔分子筛通常采用“自上而下法”和“自下而上法”进行制备。本文主要对近年来等级孔分子筛的合成方法进行梳理，并重点介绍了具有较高应用潜力的“自上而下法”。综合评述了等级孔分子筛在催化应用中的扩散过程强化研究，指出等级孔分子筛在提升催化性能方面（如活性、选择性、稳定性等）具有独特优势。通过在分子筛骨架中引入等级孔道，缩短晶内扩散路程，减少传质扩散限制，减少二次副反应和积炭。此外，等级孔道结构也有利于金属活性物种的稳定，在催化反应中抑制其烧结，增加了负载型分子筛催化剂的稳定性。最后，总结了等级孔分子筛的独特优势（强化内扩散性能和提升分子筛内部中心利用率），并对等级孔分子筛的制备方法和绿色生产进行展望。

关键词: 等级孔分子筛, 传质限制, 扩散强化, 催化