27Al MAS NMR Studies of HBEA Zeolite at Low to High Magnetic Fields,The Journal of Physical Chemistry C

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27Al MAS NMR Studies of HBEA Zeolite at Low to High Magnetic Fields
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2017-05-17 00:00:00 , DOI: 10.1021/acs.jpcc.7b03517
Jian Zhi Hu ₁ , Chuan Wan ₁ , Aleksei Vjunov ₁ , Meng Wang ₁ , Zhenchao Zhao ₁ , Mary Y. Hu ₁ , Donald M. Camaioni ₁ , Johannes A. Lercher _{1,

2}

Affiliation

²⁷Al single pulse (SP) MAS NMR spectra of HBEA zeolites with high Si/Al ratios of 71 and 75 were obtained at three magnetic field strengths of 7.05, 11.75, and 19.97 T. High field ²⁷Al MAS NMR spectra acquired at 19.97 T show significantly improved spectral resolution, resulting in at least two well-resolved tetrahedral-Al NMR peaks. Based on the results obtained from ²⁷Al MAS and MQMAS NMR acquired at 19.97 T, four different quadrupole peaks are used to deconvolute the ²⁷Al SP MAS spectra acquired at various fields by using the same set of quadrupole coupling constants, asymmetric parameters and relative integrated peak intensities for the tetrahedral Al peaks. The line shapes of individual peaks change from typical quadrupole line shape at low field to essentially symmetrical line shapes at high field. We demonstrate that, for fully hydrated HBEA zeolites, the effect of second-order quadrupole interaction can be ignored, and quantitative spectral analysis can be performed by directly fitting the high field spectra using mixed Gaussian/Lorentzian line shapes. Also, the analytical steps described in our work allow direct assignment of spectral intensity to individual Al tetrahedral sites (T-sites) of zeolite HBEA. Finally, the proposed concept is suggested to be generally applicable to other zeolite framework types, thus allowing a direct probing of Al distributions by NMR spectroscopic methods in zeolites with high confidence.

中文翻译：

HBEA沸石在低至高磁场下的²⁷ Al MAS NMR研究

在7.05、11.75和19.97 T的三个磁场强度下获得了具有高Si / Al比71和75的HBEA沸石的²⁷ Al单脉冲（SP）MAS NMR光谱。在19.97 T处获得的高磁场²⁷ Al MAS NMR光谱显示出显着改善的光谱分辨率，导致至少两个良好分辨的四面体-Al NMR峰。根据从19.97 T下获得的²⁷ Al MAS和MQMAS NMR获得的结果，使用四个不同的四极峰对²⁷进行去卷积Al SP MAS光谱是通过使用同一组四极杆耦合常数，非对称参数和四面体Al峰的相对积分峰强度在各个场获得的。各个峰的线形从低场的典型四极线形状变为高场的基本上对称的线形状。我们证明，对于完全水合的HBEA沸石，可以忽略二阶四极相互作用的影响，并且可以通过使用混合的高斯/洛伦兹线形直接拟合高场光谱来进行定量光谱分析。同样，我们工作中描述的分析步骤允许将光谱强度直接分配给HBEA沸石的各个Al四面体位点（T位）。最后，建议的概念建议普遍适用于其他沸石骨架类型，

更新日期：2017-06-03

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