Qin Zhengxing, Zeng Shu, Melinte Georgian, Bučko Tomáš, Badawi Michael, Shen Yanfeng, Gilson Jean-Pierre, Ersen Ovidiu, Wei Yingxu, Liu Zhongmin, Liu Xinmei, Yan Zifeng, Xu Shutao, Valtchev Valentin, Mintova Svetlana
State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum (East China), Qingdao, 266580, China.
National Engineering Laboratory for Methanol to Olefins, Dalian National Laboratory for Clean Energy, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, China.
Adv Sci (Weinh). 2021 Sep;8(17):e2100001. doi: 10.1002/advs.202100001. Epub 2021 Jul 4.
Hierarchical zeolites are regarded as promising catalysts due to their well-developed porosity, increased accessible surface area, and minimal diffusion constraints. Thus far, the focus has been on the creation of mesopores in zeolites, however, little is known about a microporosity upgrading and its effect on the diffusion and catalytic performance. Here the authors show that the "birth" of mesopore formation in faujasite (FAU) type zeolite starts by removing framework T atoms from the sodalite (SOD) cages followed by propagation throughout the crystals. This is evidenced by following the diffusion of xenon (Xe) in the mesoporous FAU zeolite prepared by unbiased leaching with NH F in comparison to the pristine FAU zeolite. A new diffusion pathway for the Xe in the mesoporous zeolite is proposed. Xenon first penetrates through the opened SOD cages and then diffuses to supercages of the mesoporous zeolite. Density functional theory (DFT) calculations indicate that Xe diffusion between SOD cage and supercage occurs only in hierarchical FAU structure with defect-contained six-member-ring separating these two types of cages. The catalytic performance of the mesoporous FAU zeolite further indicates that the upgraded microporosity facilitates the intracrystalline molecular traffic and increases the catalytic performance.
分级沸石由于其发达的孔隙率、增加的可及表面积和最小的扩散限制而被视为有前景的催化剂。到目前为止，重点一直是在沸石中创建中孔，然而，关于微孔升级及其对扩散和催化性能的影响却知之甚少。在此，作者表明，八面沸石（FAU）型沸石中孔形成的“诞生”始于从方钠石（SOD）笼中去除骨架T原子，随后在整个晶体中扩展。与原始FAU沸石相比，通过用NH₄F进行无偏浸出制备的中孔FAU沸石中氙（Xe）的扩散情况证明了这一点。提出了Xe在中孔沸石中的一种新扩散途径。氙首先穿透开放的SOD笼，然后扩散到中孔沸石的超笼中。密度泛函理论（DFT）计算表明，Xe在SOD笼和超笼之间的扩散仅发生在具有包含缺陷的六元环将这两种类型的笼隔开的分级FAU结构中。中孔FAU沸石的催化性能进一步表明，升级后的微孔有利于晶内分子传输并提高催化性能。
