X-ray absorption spectroscopic study on the structure and crystallization of Ga-containing MFI-type zeolites

verfasst von: Peter Behrens, Hendrik Kosslick, Anh Tuan Vu Anh Tuan, Michael Fröba, Frank Neissendorfer
Abstract: The local environment of the Ga atoms in a series of gallosilicates with MFI structure as well as in the dried synthesis gel has been investigated by GaK XANES and EXAFS. In fully crystallized gallosilicate MFI samples, Ga is tetrahedrally coordinated by oxygen atoms with a GaO bond distance of 1.83 Å. Lack of order beyond the first coordination shell is in agreement with Ga located in several different crystallographic sites of the zeolite-type framework. For the gel, the same oxygen coordination is observed for the first coordination shell. As expected for the amorphous gel, no order beyond the first coordination shell is detected. Thus, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) cannot differentiate between tetrahedrally coordinated Ga atoms in a gel phase and Ga atoms incorporated into the framework. Inspection of a series of samples prepared with different crystallization times and with Si Ga ratios>40 show that during crystallization framework and extra-framework Ga remain in tetrahedral coordination. A sample with a low Si Ga ratio of 19 in the gel, a value far below the so far observed maximum Ga framework content of Si Ga≈40, contains also octahedral Ga after prolonged hydrothermal treatment. A quantitative evaluation shows that extra-framework Ga in gallosilicate MFI samples occurs in both tetrahedral and octahedral coordination. This result on the nature of extra-framework Ga is of importance, since these Ga species are believed to play a decisive role in catalytic processes on gallosilicate MFI-type solids.
Externe Organisation(en): Universität Konstanz
Leibniz-Institut für Katalyse e. V. an der Universität Rostock (LIKAT)
Universität Hamburg
Universität Potsdam
Typ: Artikel
Journal: Microporous Materials
Band: 3
Seiten: 433-441
Anzahl der Seiten: 9
ISSN: 0927-6513
Publikationsdatum: 01.1995
Publikationsstatus: Veröffentlicht
Peer-reviewed: Ja
ASJC Scopus Sachgebiete: Allgemeine Chemie, Allgemeine Materialwissenschaften, Allgemeiner Maschinenbau
Elektronische Version(en): https://doi.org/10.1016/0927-6513(94)00054-Y (Zugang: Geschlossen)

BibTeX

@article{b6c98ce624774aaeb3f95b81baf60ff8,
title = "X-ray absorption spectroscopic study on the structure and crystallization of Ga-containing MFI-type zeolites",
abstract = "The local environment of the Ga atoms in a series of gallosilicates with MFI structure as well as in the dried synthesis gel has been investigated by GaK XANES and EXAFS. In fully crystallized gallosilicate MFI samples, Ga is tetrahedrally coordinated by oxygen atoms with a GaO bond distance of 1.83 {\AA}. Lack of order beyond the first coordination shell is in agreement with Ga located in several different crystallographic sites of the zeolite-type framework. For the gel, the same oxygen coordination is observed for the first coordination shell. As expected for the amorphous gel, no order beyond the first coordination shell is detected. Thus, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) cannot differentiate between tetrahedrally coordinated Ga atoms in a gel phase and Ga atoms incorporated into the framework. Inspection of a series of samples prepared with different crystallization times and with Si Ga ratios>40 show that during crystallization framework and extra-framework Ga remain in tetrahedral coordination. A sample with a low Si Ga ratio of 19 in the gel, a value far below the so far observed maximum Ga framework content of Si Ga≈40, contains also octahedral Ga after prolonged hydrothermal treatment. A quantitative evaluation shows that extra-framework Ga in gallosilicate MFI samples occurs in both tetrahedral and octahedral coordination. This result on the nature of extra-framework Ga is of importance, since these Ga species are believed to play a decisive role in catalytic processes on gallosilicate MFI-type solids.",
keywords = "Extended X-ray absorption fine structure, Extra-framework gallium, Gallosilicate, MFI, X-ray absorption near edge structure",
author = "Peter Behrens and Hendrik Kosslick and {Vu Anh Tuan}, {Anh Tuan} and Michael Fr{\"o}ba and Frank Neissendorfer",
note = "Funding information: We thank Hasylab Desy (Hamburg, Germany) for allocating beamtime and the Hasylab staff for technical assistance. Help during the measurements from Stefanie Assmann (Universit~t Konstanz) and Karin Lochte (Universitfit Hamburg) is gratefully acknowledged. M.F. thanks the Alexander von Humboldt Foundation for a Feodor Lynen Research Fellowship.",
year = "1995",
month = jan,
doi = "10.1016/0927-6513(94)00054-Y",
language = "English",
volume = "3",
pages = "433--441",
journal = "Microporous Materials",
issn = "0927-6513",
publisher = "Elsevier",
number = "4-5",
}