Exploring the Na+ Locations and Al Distributions in SSZ-39 Zeolite by Solid-State NMR Spectroscopy and DFT Calculations

• Published in: Bopuxue zazhi Vol. 38; no. 4; pp. 543 - 551
• Main Authors: Han-di CHEN, Hai-yu KONG, Zhen-chao ZHAO, Wei-ping ZHANG
• Format: Journal Article
• Language: Chinese
• Published: Science Press 01.12.2021
• Subjects: al distribution; cation location; density functional theory (dft) calculations; solid-state nuclear magnetic resonance; ssz-39 zeolite
• ISSN: 1000-4556
• DOI: 10.11938/cjmr20212906

The catalytic performance of zeolite SSZ-39 with AEI structure is significantly affected by the locations of its extra-framework cation and aluminum distributions. The AEI cage contains three crystallographically inequivalent T sites that tend to be substituted by aluminum. In this work, the Na+ locations and Al distributions in Na-SSZ-39 with different Si/Al ratios were studied by 27Al/23Na MQ MAS NMR spectroscopy together with density functional theory (DFT) calculations. For isolated Al substitution, the T3 site was found to be preferentially occupied by Al, and Na+ was mainly located in the 6-MR (SIIa0) or 8-MR (SIII'a0) sites of the AEI cage, although the priority of SIII'a0 site was slightly higher, and minor Na+ was located inside the hexagonal prism (SIa0). For paired Al substitution, stable AlSiSiAl structure was found to be located in 6-MR, and the corresponding Na+ cations were located at SIIa1 and SIII'a1 sites, respectively. In post-modified zeolites with partial destruction of the framework stru