Direct solid-state NMR spectroscopic evidence for the NH 4AlF4 crystalline phase derived from zeolite HY dealuminated with ammonium hexafluorosilicate

Hsien Ming Kao, Pai Ching Chang

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13 Scopus citations

Abstract

Multinuclear 1H, 19F, and 27Al MAS (magic angle spinning) and corresponding 2D HETCOR (heteronuclear correlation) NMR spectroscopy, in combination with powder XRD measurements, provide the direct evidence for the NH4AlF4 crystalline phase, which was formed from zeolite HY dealuminated with an aqueous (NH4) 2-SiF6 solution at 80 °C. The NH4AlF 4 crystalline phase exhibits a characteristic second-order quadrupolar-induced 27Al NMR line shape spreading from 0 to -90 ppm (in a magnetic field of 11.7 T) and two 19F resonances at -151 and -166 ppm in the 19F NMR spectrum. An 27Al quadrupolar coupling constant (CQ) of 9.5 MHz and an asymmetry parameter (ν) of 0.1 were identified, for the first time, for the NH4AlF 4 crystalline phase observed. On the basis of the 19F{27Al} TRAPDOR (transfer population in double resonance) NMR results, the 19F resonances at -151 and -166 ppm are therefore assigned to 19F spins associated with the fluorines in the terminal Al-F and the bridging Al-F-Al groups, respectively.

Original languageEnglish
Pages (from-to)19104-19107
Number of pages4
JournalJournal of Physical Chemistry B
Volume110
Issue number39
DOIs
StatePublished - 5 Oct 2006

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