Detailed interpretation of the 29Si and 27Al high-field MAS n.m.r. spectra of zeolites offretite and omega

Fyfe, C. A.; Gobbi, G. C.; Kennedy, Gordon J.; Graham, James D.; Ozubko, R. S.; Murphy, William J.; Bothner‐By, Aksel A.; Dadok, Josef; Chesnick, A. Scott

doi:10.1016/0144-2449(85)90027-2

Cited by 85 publications

(35 citation statements)

References 15 publications

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“…However the ability to resolve crystallographically distinct sites is limited compared to 29Si asa result of the smaller range of isotropic chemical shifts and broader MAS NMR resonances for 27Al. InAl (6) Al(4) stances of the detection of inequivalent aluminium sites do exist, including ZSM-5 [125,126] and mazzite (zeolite Q) [127][128][129][130], which has two Al(4) sites (Fig. 17).…”

Section: Zeolitesmentioning

confidence: 99%

Application of27Al NMR techniques to structure determination in solids

1993

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Abstraer. There have been great improvements in the quality of 27A1 NMR spectra from solids over the last decade. The impact of this technique on structure determination fora wide range of solids is briefly reviewed. Emphasis is placed on the effects arising from the presence of the quadrupolar interaction and strategies that allow unambiguous spectral interpretation. It is demonstrated that in addition to the chemical shift, the quadrupolar interaction itself can be a rich source of local information about solids. The insight obtalned from 27A1 NMR hato atomic level structure often contains surprises, such that previous models of structure and properties have to be reassessed.

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Section: Zeolitesmentioning

confidence: 99%

Application of27Al NMR techniques to structure determination in solids

1993

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“…As a result, only gross features of the spectrum could be observed. Fyfe et al (1985) were able to improve the resolution of the 27A1 MAS NMR spectrum for zeolite omega (MAZ) by using a higher magnetic field and a higher rate of spinning. The spectrum showed two signals which were indicative of the presence of two non-equivalent tetrahedral A1 sites.…”

Section: Magic Angle Spinning Nmrmentioning

confidence: 99%

Zeolite crystallography. Structure determination in the absence of conventional single-crystal data

McCusker¹

1991

Acta Cryst Sect A

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Zeolite molecular sieves are a class of aluminosilicates whose technologically important properties are intimately related to their structures. Since most synthetic zeolites are only available as powders and not as single crystals, conventional crystallographic techniques cannot be used to solve their structures. The crystallographic diffÉculties are exacerbated by the pseudosymmetry, faulting, disorder and impurity problems, which are relatively common in zeolite materials. Over the years, zeolite crystallographers have developed a number of approaches to these problems and these are discussed. The techniques include informed model building, various computer approaches to model generation, application of direct methods to powder data, microcrystalline diffraction and exploitation of magic angle spinning NMR and electron microscopy. Usually a number of methods are combined to construct a framework structure model and to test it for feasibility. Once a reasonable model has been produced, Rietveld refinement will not only confirm (or reject) the framework proposal but also reveal further details of the structure. Although the techniques described were developed for application to zeolite structures, many can probably be applied to other systems.

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“…The 1 H MAS NMR technique allows us to measure the concentration of different types of surface hydroxyl groups, since the intensity of the corresponding 1 H MAS NMR signals is directly proportional to the concentration of the resonating nuclei [43,44]. The number of Brönsted acid sites per unit cell was estimated based on the framework Si/Al ratio measured by 29 Si MAS NMR spectra and the chemical formula of the unit cell of the HZSM-5 zeolite [45]. The number of Brönsted acid sites per unit cell of the 6Mo/HZSM-5 catalysts after calcinations for different durations of time was estimated by comparing the peak areas of the 1 H MAS NMR spectra with those of the corresponding parent zeolite.…”

Section: Catalyst Characterizationmentioning

confidence: 99%