从<sup>23</sup> Na固态NMR光谱和DFT计算得出SSZ-13沸石中的Al分布图。,The Journal of Physical Chemistry C

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从²³ Na固态NMR光谱和DFT计算得出SSZ-13沸石中的Al分布图。
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2018-04-17 00:00:00 , DOI: 10.1021/acs.jpcc.8b01423
Zhenchao Zhao ₁ , Youdong Xing ₁ , Shihan Li ₁ , Xiangju Meng ₂ , Feng-shou Xiao ₂ , Robert McGuire ₃ , Andrei-Nicolae Parvulescu ₃ , Ulrich Müller ₃ , Weiping Zhang ₁

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SSZ-13沸石中Al的分布和相应的非骨架阳离子的位置对其催化和吸附性能有重大影响。本文中，我们通过结合²³ Na MQ MAS NMR光谱和DFT计算，阐明了在一系列Si / Al比为4至48的Na-SSZ-13沸石中阐明Na ⁺位置和相关Al分布的可行性。由于CHA笼中仅存在一个晶体学上不等价的T位点，因此孤立的Al和Al对（六元体系中的Al–O–Si–O–Si–O–Al）和（Al–O–Si–O–Al）对清楚地区分了环（MR）分布和相应的Na ⁺位置。在高硅Na-SSZ-13沸石中，Na ⁺离子主要位于6-MR SIIa0位点，与CHA笼中的一个Al取代相对应。但是，即使Si / Al比为48，仍可观察到少量的6-MR中的Al对，分别对应于位于6-MR SIIa1和8-MR SIII'a1位的两个Na ⁺离子。在CHA笼中有更多的Al取代，在不同SII位点之间具有较高迁移率的一部分Na ⁺离子可能会导致SIII'b位点。在富含Al的SSZ-13沸石（Si / Al = 4）中，Si（2Al）和Si（3Al）的存在可能导致Na ⁺位于6-MR SIIa2上，其中²³Na NMR信号表现出相对较大的四极相互作用，并且在8-MR SIII'a2处，NMR信号与SIII'a1位点重叠。这种方法可能会扩展其在判别其他沸石中Al分布方面的应用，以更深入地了解结构和性能之间的关系，以供其应用于催化和吸附中。

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Mapping Al Distributions in SSZ-13 Zeolites from 23Na Solid-State NMR Spectroscopy and DFT Calculations

Al distributions and locations of corresponding nonframework cations in SSZ-13 zeolites have significant impact on their catalytic and adsorption properties. Herein, we demonstrate the feasibility of elucidating Na⁺ locations and correlated Al distributions in a series of Na-SSZ-13 zeolites with Si/Al ratios ranging from 4 to 48 by combining ²³Na MQ MAS NMR spectroscopy and DFT calculations. As only one crystallographically inequivalent T site exists in CHA cages, the isolated Al and the Al pair (Al–O–Si–O–Si–O–Al) and (Al–O–Si–O–Al) in 6-membered ring (MR) distributions and the corresponding Na⁺ locations are clearly discriminated. In the high-silica Na-SSZ-13 zeolite, Na⁺ ions are mainly located at the 6-MR SIIa0 site corresponding to one Al substitution in the CHA cage. However, a small amount of the Al pair in 6-MR is still observable even with an Si/Al ratio of 48, corresponding to two Na⁺ ions located at 6-MR SIIa1 and 8-MR SIII’a1 sites, respectively. With more Al substitutions in the CHA cage, a portion of Na⁺ ions with high mobility among different SII sites may result in the SIII’b site. In Al-rich SSZ-13 zeolite (Si/Al = 4), the presence of Si(2Al) and Si(3Al) may lead to Na⁺ being located at 6-MR SIIa2, with ²³Na NMR signals exhibiting relatively large quadrupolar interactions, and at 8-MR SIII’a2, with NMR signals overlapped with that of the SIII’a1 site. This approach may expand its application in discrimination of Al distributions in other zeolites to gain deeper understanding of the relationship between the structure and the property for their applications in catalysis and adsorption.

更新日期：2018-04-17

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