Preparation of ferrisilicate ZSM-5 molecular sieves

Szostak, R.; Thomas, T. L.

doi:10.1016/0021-9517(86)90131-4

Cited by 122 publications

(32 citation statements)

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“…Accordingly, in the partially Fe-substituted mordenite, a new Si-O-Fe bond vibration could be found near 668 cm −1 , which is absent in the IR spectrum of normal mordenite. Szostak and Thomas [3,36] have found that the Si-O-Fe symmetric stretching vibration occurs at 679 and 656 cm −1 in the sodalite and ZSM-5 system, respectively. We also reported similar results previously that the absorption originating from the vibration of Fe-O-Si is observed at 668 cm −1 in the spectra of ferrisilicate LTL [37].…”

Section: Resultsmentioning

confidence: 98%

“…ESR is predominantly used to check the g=4.3 signal in order to confirm the tetrahedral substitution. The signal at g=2.0 is known to be strongly affected by the water vapor content, and Park and Chon [41] reported that it diminishes with water vapor for FAPO-5, whereas it grows with water vapor for Fe-ZSM-5 [36]. The UV-vis spectra of the as-synthesized Fe-substituted mordenite samples with different iron content are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Hydrothermal synthesis and characterization of Fe(III)-substituted mordenites

Jang

Ahn

2008

Korean J. Chem. Eng.

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Fe-substituted mordenites were synthesized hydrothermally, partially substituting iron atoms for the framework aluminum of mordenite. XRD, SEM, IR, UV-VIS DRS, ESR, XAS, and catalytic activity studies provided the evidence of Fe 3+ present in the zeolite framework. The framework IR bands were shifted to lower frequencies as Fe 3+ ions incorporated into the lattice, and a new Si-O-Fe bond vibration was located near 668 cm −1 . The presence of a signal at g=4.3 in the ESR spectra was assigned to Fe 3+ isomorphously substituted in the tetrahedral position. EXAFS at the Fe K-edge revealed that the Fe 3+ ions were present in the zeolite framework in a four-fold coordination with an average Fe-O distance of 1.86 Å. In the UV-vis spectra, an absorption was observed at 375.7 nm which was assigned to the presence of Fe 3+ in the zeolite framework. A toluene alkylation study reflected that the acidity strength of mordenite is weakened due to the presence of lattice iron species.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Hydrothermal synthesis and characterization of Fe(III)-substituted mordenites

Jang

Ahn

2008

Korean J. Chem. Eng.

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“…[1,2] This reaction is catalysed by Fe-MFI zeolites [3] (Fesilicalite and Fe-ZSM-5), which are synthesised with accommodation of small amounts of Fe 3 ions in framework positions. [4,5] The catalyst becomes active only after severe thermal treatment (up to 1100 K), which causes the migration of iron to extraframework positions and its reduction to Fe 2 .…”

Section: Introductionmentioning

confidence: 99%

“…This shift is small for all components (2 ± 3 cm Figure 3 illustrates the effect of decreasing P NO on the nitrosyl bands obtained on aluminium-free Fe-silicalite samples activated at 773 and 1073 K and on a Fe-ZSM-5 sample activated at 1073 K. The spectra obtained for Fe-silicalite activated at 773 K were extensively discussed and assigned in previous works. [10,11,15] The bands observed are due to extraframework Fe 2 species generated from framework Fe 3 (ÀOÀSi) 4 by thermal treatment. Apart from minor features (see ref.…”

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confidence: 95%

Anchoring Fe Ions to Amorphous and Crystalline Oxides: A Means To Tune the Degree of Fe Coordination

Berlier¹,

Bonino²,

Zecchina³

et al. 2003

ChemPhysChem

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We report on an IR spectroscopic study on the room-temperature adsorption of NO on different iron(II)-containing siliceous matrices. Fe2+ hosted inside the channels of MFI-type zeolites (Fe-ZSM-5 and Al-free Fe-silicalite) exhibits pronounced coordinative unsaturation, as witnessed by the capability to form, at 300 K, [Fe2-(NO)], [Fe2+(NO)2] and [Fe2+(NO)3] complexes with increasing NO equilibrium pressure. Fe2+ hosted on amorphous supports (high surface area SiO2 and MCM-41) sinks more deeply into the surface of the siliceous support and thus exhibits less pronounced coordinative unsaturation: only [Fe2+(NO)2] complexes were observed, even at the highest investigated NO equilibrium pressures. Activation at higher temperature (1073 K) of the Al-free Fe-silicalite sample resulted in the appearance of Fe2+ species similar to those observed on SiO2 and MCM-41, and this suggests that local (since not detectable by X-ray diffraction) amorphisation of the environment around Fe2+ anchoring sites occurs. The fact that this behaviour is not observed on the Fe-ZSM-5 sample activated at the same temperature suggests that framework Al species (and their negatively charged oxygen environment) have an important role in anchoring extraframework Fe2+ species. Such an anchoring phenomenon will prevent a random migration of iron species, with subsequent aggregation and loss of coordinative unsaturation. These observations can thus explain the higher catalytic activity of the Fe-ZSM-5 system in one-step benzene to phenol conversion when compared with the parent, Al-free, Fe-silicalite system with similar Fe content. The nature of the support and the activation temperature can therefore be used as effective means to tune the degree of Fe coordination.

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“…MFI (Mobil Five) type molecular sieves are well-known crystalline microporous solids that possesses a network based on near-circular straight (5.4-5.6 Å) and elliptical sinusoidal (5.1-5.5 Å) channels both defined by 10-membered rings. The isomorphous substitution of Si 4+ ions by other tetrahedrally coordinated elements in MFI structure [3][4][5][6][7][8] have opened a new class of compounds of academic and industrial importance. By virtue of higher electronegativity, atomic size and strong acidity, the incorporation of Sn (IV) in the tetrahedral silica frameworks possessing zeolitic structures led to yield promising sorbent [9] and catalysts [9][10][11][12][13][14][15][16] for various reactions of academic and commercial importance.…”

Section: Introductionmentioning

confidence: 99%