Chinese Journal of Magnetic Resonance ›› 2021, Vol. 38 ›› Issue (4): 543-551.doi: 10.11938/cjmr20212906

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

Han-di CHEN,Hai-yu KONG,Zhen-chao ZHAO,Wei-ping ZHANG*()   

  1. State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China
  • Received:2021-04-11 Online:2021-12-05 Published:2021-05-10
  • Contact: Wei-ping ZHANG E-mail:wpzhang@dlut.edu.cn

Abstract:

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 structure, some free Na+ cations were found to form distinct SIII'b sites. This study deepened the understanding on the structure-reactivity correlation of SSZ-39 zeolite and provided insights into how to fine-tune its catalytic performance.

Key words: solid-state nuclear magnetic resonance, SSZ-39 zeolite, Al distribution, cation location, density functional theory (DFT) calculations

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