Understanding the fundamentals of microporosity upgrading in zeolites: increasing diffusion and catalytic performances

Zhengxing Qin (1) , Shu y Zeng (2, 3) , Georgian Melinte (4) , Tomáš Bučko (5, 6) , Michael Badawi (7) , Yanfeng Shen (1) , Jean‐pierre Gilson (8) , Ovidiu Ersen (4) , Yingxu Wei (2) , Zhongmin Liu (2, 3) , Xinmei Liu (1) , Zifeng Yan (1) , Shutao Xu (2) , Valentin Valtchev (8) , Svetlana Mintova (8, 1)

1 China University of Petroleum
2 DICP - Dalian Institute of Chemical Physics
3 UCAS - University of Chinese Academy of Sciences [Beijing]
4 IPCMS - Institut de Physique et Chimie des Matériaux de Strasbourg
5 Department of Biochemistry, Faculty of Natural Sciences, Comenius University in Bratislava
6 SAS - Slovak Academy of Sciences
7 LPCT - Laboratoire de Physique et Chimie Théoriques
8 LCS - Laboratoire catalyse et spectrochimie

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 NH4 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.

Mots clés: Zeolites; Microporosity upgrading; Molecular diffusion; HP 129 Xe NMR; DFT calculation

Domaines: Chimie

Zhengxing Qin, Shu y Zeng, Georgian Melinte, Tomáš Bučko, Michael Badawi, et al.. Understanding the fundamentals of microporosity upgrading in zeolites: increasing diffusion and catalytic performances. Advanced Science, 2021, 8 (17), pp.2100001. ⟨10.1002/advs.202100001⟩. ⟨hal-03416078⟩