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In situ high-temperature ESR characterization of FeZSM-5 and FeSAPO-34 catalysts in flowing mixtures of NO, C3H6, and O2

In situ high-temperature ESR characterization of FeZSM-5 and FeSAPO-34 catalysts in flowing... In situ ESR of FeHZSM-5 shows that samples made by sublimation of FeCl3 contain mainly ferric ions in tetrahedral and distorted tetrahedral sites. Above 200°C these ions do not chemisorb water, which confirms the resistance to activity deterioration by water vapor claimed for FeHZSM-5, when used in SCR of NOx. The number of ESR-active Fe3+ ions decreases when moving from strongly oxidizing conditions towards stoichiometry at 500°C. In more reducing atmospheres, i.e., when excess reductant is present, the exposure produces an agglomerated ferromagnetic species, presumably magnetite. This process is irreversible. As the trivalent dispersed iron ions are the catalytically active sites, this transformation makes Fe-containing catalysts vulnerable to accidental but irreversible transformation induced by even mildly reducing conditions. The dispersion of ferric ions in FeSAPO-34 is not as good as in FeHZSM-5 and the reactive Fe3+ in distorted tetrahedral sites is absent. Catalytic oxidation of ethane allows correlation of the EPR results with activity and stability. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Catalysis Letters Springer Journals

In situ high-temperature ESR characterization of FeZSM-5 and FeSAPO-34 catalysts in flowing mixtures of NO, C3H6, and O2

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References (25)

Publisher
Springer Journals
Copyright
Copyright © 1998 by Kluwer Academic Publishers
Subject
Chemistry; Physical Chemistry; Industrial Chemistry/Chemical Engineering; Catalysis; Pharmacy
ISSN
1011-372X
eISSN
1572-879X
DOI
10.1023/A:1019002322340
Publisher site
See Article on Publisher Site

Abstract

In situ ESR of FeHZSM-5 shows that samples made by sublimation of FeCl3 contain mainly ferric ions in tetrahedral and distorted tetrahedral sites. Above 200°C these ions do not chemisorb water, which confirms the resistance to activity deterioration by water vapor claimed for FeHZSM-5, when used in SCR of NOx. The number of ESR-active Fe3+ ions decreases when moving from strongly oxidizing conditions towards stoichiometry at 500°C. In more reducing atmospheres, i.e., when excess reductant is present, the exposure produces an agglomerated ferromagnetic species, presumably magnetite. This process is irreversible. As the trivalent dispersed iron ions are the catalytically active sites, this transformation makes Fe-containing catalysts vulnerable to accidental but irreversible transformation induced by even mildly reducing conditions. The dispersion of ferric ions in FeSAPO-34 is not as good as in FeHZSM-5 and the reactive Fe3+ in distorted tetrahedral sites is absent. Catalytic oxidation of ethane allows correlation of the EPR results with activity and stability.

Journal

Catalysis LettersSpringer Journals

Published: Oct 13, 2004

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