Local Structure of Cationic Sites in Dehydrated Zeolites Inferred from Al-27 Magic-Angle Spinning NMR and Density Functional Theory Calculations. A Study on Li-, Na-, and K-Chabazite
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Datum publikování
2016
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American Chemical Society
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High-resolution Al-27 magic-angle spinning (MAS) NMR spectroscopy of dehydrated M-forms (M = Li, Na, and K) of chabazite in tandem with density functional theory calculations are employed to study the quadrupolar interaction of Al-27 nuclei in dehydrated zeolites and to understand the corresponding high-resolution Al-27 MAS NMR spectra. We show that the broadening of the Al-27 NMR signal in dehydrated zeolites occurs predominantly because of the deformation of the local structure of AlO4- tetrahedra caused by the binding of M+ to the zeolite framework. This deformation increases with the decreasing diameter of the cations from K+ to Li+. The influence of water in hydrated zeolites is limited only to prevent a strong coordination of the M+ cation to O atoms of the AlO4- tetrahedron, but there is no "averaging" effect concerning the local electrostatic field due to molecular motion of water molecules. Our results show that the Al-27 NMR parameters in dehydrated zeolites can be calculated accurately enough to allow the description of the local structure of AlO4- tetrahedra in dehydrated zeolites and to infer the local structure of the sites accommodating the extraframework M+ cations.
Rozsah stran
p. 14216-14225
ISSN
1932-7447
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Journal of Physical Chemistry C, volume 120, issue: 26
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solid-state nmr, high-resolution al-27, approximate coulomb potentials, nuclear-magnetic-resonance, aluminum distribution, crystallographic determination, electron-densities, NMR reakcí v pevné fázi, vysoké rozlišení al-27, přibližný coulombovský potenciál, nukleární magnetická rezonance, distribuce hliníku, krystalografické stanovení, elektronová hustota