Probing ge distribution in zeolite frameworks by post-synthesis introduction of fluoride in as-made materials

Xiaolong Liu, Ugo Ravon, Françoise Bosselet, Gérard Bergeret, Alain Tuel

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31 Scopus citations

Abstract

A new method has been developed to introduce fluoride in the structure of as-made germanium-containing zeolites prepared under pure alkaline media. Incorporation of fluoride species occurs without modification of the framework composition (Si/Ge ratio) and of the crystallinity, as evidenced by X-ray diffraction and electron microscopy. After incorporation, 19F solid-state NMR has been used to probe the location and distribution of Ge atoms in the framework. In the case of ITQ-13 and ITQ-17, which can be prepared from both hydroxide and fluoride routes, incorporated F anions are located in the same structural units as those occupied when zeolites are prepared in the presence of fluoride. In the case of ITQ-22 and ITQ-24, fluoride goes mainly in D4R units, which appear to be in the most energetically favorable positions for these zeolites. All experiments clearly show that zeolites prepared in the absence of fluoride in the synthesis medium are enriched in germanium, compared to the same materials obtained from F-containing gels. Moreover, Ge plays a strong structure-directing role by replacing Si atoms preferentially in D4R, leading to zeolites with mainly [4Si, 4Ge] units in the framework. In the particular case of ITQ-22, a new line observed around -2 ppm in 19F NMR spectra has been tentatively assigned to [3Si, 5Ge] D4R units, which corroborates the structural data obtained via X-ray diffraction. © 2012 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)3016-3022
Number of pages7
JournalChemistry of Materials
Volume24
Issue number15
DOIs
StatePublished - Jul 20 2012

ASJC Scopus subject areas

  • Materials Chemistry
  • Chemical Engineering(all)
  • Chemistry(all)

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