波谱学杂志 ›› 2021, Vol. 38 ›› Issue (4): 543-551.doi: 10.11938/cjmr20212906

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固体核磁共振结合密度泛函理论计算研究SSZ-39分子筛的钠离子落位与铝分布

陈翰迪,孔海宇,赵侦超,张维萍*()   

  1. 大连理工大学 化工学院 精细化工国家重点实验室, 辽宁 大连 116024
  • 收稿日期:2021-04-11 出版日期:2021-12-05 发布日期:2021-05-10
  • 通讯作者: 张维萍 E-mail:wpzhang@dlut.edu.cn
  • 基金资助:
    国家自然科学基金资助项目(21872017)

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

摘要:

具有AEI结构的SSZ-39分子筛的骨架外阳离子落位和铝分布对其催化性能影响显著.AEI笼中有三个结晶学不等价位,且铝取代T位具有一定的倾向性.本文结合固体核磁共振(NMR)技术(27Al/23Na MQ MAS NMR),以及密度泛函理论(DFT)计算,研究了不同硅铝比Na-SSZ-39分子筛中的Na+落位和铝分布.在孤立铝分布的情况下,铝原子优先占据于T3位,Na+主要落位于AEI笼中的SIIa0和SIII'a0位点上,其中SIII'a0位点的优先度较高,此外少部分Na+还落位于六棱柱内部的SIa0.当铝对存在时,AlSiSiAl分布的铝对占据六元环的对位(T3-T3),对应的Na+分别落位于SIIa1和SⅢ'a1位点.随着分子筛结构的部分破坏,游离的Na+可能形成明显的SIII'b位点.本文可加深对SSZ-39分子筛构效关系的理解,为更好地调控催化性能奠定基础.

关键词: 固体核磁共振, SSZ-39分子筛, 铝分布, 阳离子落位, 密度泛函理论(DFT)计算

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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