Changes in states of substituted iron in microporous (MFI analogue) and mesoporous (MCM-41) hosts exposed to redox conditions

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Abstract

Iron was incorporated into microporous MFI analogue (ZSM-5, Si/Fe ∼ 200 and FER, Si/Fe = 16) and mesoporous MCM-41 hosts of different preparations (Si/Fe ∼ 100 and 20, respectively). Samples were characterized by in situ Mössbauer spectroscopy under various conditions. Framework (FW) and extra-framework (EFW) sites can be distinguished in relation with strict three-dimensional (3D) crystallinity of the structure. In addition, in the microporous ZSM-5 system occurrence of Fe4+ oxidation state is hypothesized and reversible Fe4+ ↔ Fe3+ transformation is presumed for a minor portion of iron. Spectra of Fe-FER are interpreted in terms of dynamic formation and decomposition of Fe FW-O-FeEFW dinuclear centres. In the mesoporous systems, the partly amorphous character of the pore wall is correlated with the redox behaviour and coordination of incorporated iron; larger portion of iron may take part in Fe3+ ↔ Fe2+ reversible processes and Fe 2+ may be stabilized in distorted coordination (not appearing in microporous structures).

Original languageEnglish
Pages (from-to)239-246
Number of pages8
JournalCatalysis Today
Volume110
Issue number3-4
DOIs
Publication statusPublished - Dec 30 2005

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Multicarrier modulation
Iron
Spectroscopy
Decomposition
Oxidation
Oxidation-Reduction
MCM-41

Keywords

  • Iron
  • Mössbauer spectroscopy
  • Porous hosts
  • Redox processes

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

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title = "Changes in states of substituted iron in microporous (MFI analogue) and mesoporous (MCM-41) hosts exposed to redox conditions",
abstract = "Iron was incorporated into microporous MFI analogue (ZSM-5, Si/Fe ∼ 200 and FER, Si/Fe = 16) and mesoporous MCM-41 hosts of different preparations (Si/Fe ∼ 100 and 20, respectively). Samples were characterized by in situ M{\"o}ssbauer spectroscopy under various conditions. Framework (FW) and extra-framework (EFW) sites can be distinguished in relation with strict three-dimensional (3D) crystallinity of the structure. In addition, in the microporous ZSM-5 system occurrence of Fe4+ oxidation state is hypothesized and reversible Fe4+ ↔ Fe3+ transformation is presumed for a minor portion of iron. Spectra of Fe-FER are interpreted in terms of dynamic formation and decomposition of Fe FW-O-FeEFW dinuclear centres. In the mesoporous systems, the partly amorphous character of the pore wall is correlated with the redox behaviour and coordination of incorporated iron; larger portion of iron may take part in Fe3+ ↔ Fe2+ reversible processes and Fe 2+ may be stabilized in distorted coordination (not appearing in microporous structures).",
keywords = "Iron, M{\"o}ssbauer spectroscopy, Porous hosts, Redox processes",
author = "K. L{\'a}z{\'a}r and A. Szegedi and P{\'a}ł, {Borb{\'e}ly G.} and Kotasthane, {A. N.} and P. Fejes",
year = "2005",
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T1 - Changes in states of substituted iron in microporous (MFI analogue) and mesoporous (MCM-41) hosts exposed to redox conditions

AU - Lázár, K.

AU - Szegedi, A.

AU - Páł, Borbély G.

AU - Kotasthane, A. N.

AU - Fejes, P.

PY - 2005/12/30

Y1 - 2005/12/30

N2 - Iron was incorporated into microporous MFI analogue (ZSM-5, Si/Fe ∼ 200 and FER, Si/Fe = 16) and mesoporous MCM-41 hosts of different preparations (Si/Fe ∼ 100 and 20, respectively). Samples were characterized by in situ Mössbauer spectroscopy under various conditions. Framework (FW) and extra-framework (EFW) sites can be distinguished in relation with strict three-dimensional (3D) crystallinity of the structure. In addition, in the microporous ZSM-5 system occurrence of Fe4+ oxidation state is hypothesized and reversible Fe4+ ↔ Fe3+ transformation is presumed for a minor portion of iron. Spectra of Fe-FER are interpreted in terms of dynamic formation and decomposition of Fe FW-O-FeEFW dinuclear centres. In the mesoporous systems, the partly amorphous character of the pore wall is correlated with the redox behaviour and coordination of incorporated iron; larger portion of iron may take part in Fe3+ ↔ Fe2+ reversible processes and Fe 2+ may be stabilized in distorted coordination (not appearing in microporous structures).

AB - Iron was incorporated into microporous MFI analogue (ZSM-5, Si/Fe ∼ 200 and FER, Si/Fe = 16) and mesoporous MCM-41 hosts of different preparations (Si/Fe ∼ 100 and 20, respectively). Samples were characterized by in situ Mössbauer spectroscopy under various conditions. Framework (FW) and extra-framework (EFW) sites can be distinguished in relation with strict three-dimensional (3D) crystallinity of the structure. In addition, in the microporous ZSM-5 system occurrence of Fe4+ oxidation state is hypothesized and reversible Fe4+ ↔ Fe3+ transformation is presumed for a minor portion of iron. Spectra of Fe-FER are interpreted in terms of dynamic formation and decomposition of Fe FW-O-FeEFW dinuclear centres. In the mesoporous systems, the partly amorphous character of the pore wall is correlated with the redox behaviour and coordination of incorporated iron; larger portion of iron may take part in Fe3+ ↔ Fe2+ reversible processes and Fe 2+ may be stabilized in distorted coordination (not appearing in microporous structures).

KW - Iron

KW - Mössbauer spectroscopy

KW - Porous hosts

KW - Redox processes

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