Synthesis of tin(IV) silicalites (MFI) and their characterization: A Mössbauer and MAS NMR spectroscopy study

P. Fejes, János B. Nagy, Kristóf Kovács, G. Vankó

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Abstract

The synthesis of tin(IV) (iron, chromium, gallium, indium and titanium) silicalites (MFI) and their characterization by SEM, X-ray diffraction, FTIR, Mössbauer and MAS NMR spectroscopies are reported. In order to obtain 'good quality' crystalline phases the respective metal silicates were prepared first at low pH (pH ca. 2.0) and the sols, containing the substituting metal in homogeneous dispersion at atomic level, were brought to gelation by increasing the pH to about 4.3. These precursor gels were subsequently washed thoroughly by percolation and homogenized in a ball mill. Crystallization was affected at 443 K (170°C) under static conditions. SEM and X-ray diffraction bear witness that the zeolite specimens are completely free of any amorphous phase and are highly crystalline. U.c. volumes decrease with increasing Sn (and Al) contents; an observation which is momentarily at variance with the accepted views. 29Si MAS NMR spectra taken with and without CP prove that defect sites are practically absent. Except titanium silicalite (MFI) the samples show no absorption at around 960 cm-1 in the IR framework region, supporting the view that similar absorptions observed previously also with V, Cr and other elements are due to strained T-O-Si linkages. 119Sn Mössbauer and MAS NMR spectra characterized by I.S. = -0.22 and Q.S. ca. 0 at R.T. and NMR resonance absorption at δ = -700 ppm (relative to SnO2 and tetramethyltin) respectively, prove the tetrahedral coordination of Sn4+ ions in the as synthesized Sn(Al)-ZSM-5 specimens. Standard (non-caring) calcination sets at least part of the substituting element(s) free (clearly observable on MAS NMR spectra and indicated in the 119Sn and 57Fe Mössbauer spectra as well (increase of Q.S. for Sn and both I.S. and Q.S. for Fe)). A caring calcination method which is capable to retain full crystallinity is advanced in this paper. The importance of the retention or partial loss of crystallinity is discussed from the viewpoint of heterogeneous catalysis.

Original languageEnglish
Pages (from-to)155-184
Number of pages30
JournalApplied Catalysis A: General
Volume145
Issue number1-2
Publication statusPublished - Oct 8 1996

Fingerprint

Tin
Nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance
Titanium
Calcination
Metals
Crystalline materials
Zeolites
Silicates
X ray diffraction
Scanning electron microscopy
Gallium
Indium
Ball mills
Chromium
Polymethyl Methacrylate
Gelation
Sols
Crystallization
Catalysis

Keywords

  • MAS NMR
  • Metal (Sn, Ti, Fe, etc.) silicalites
  • Mössbauer spectroscopies

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

Synthesis of tin(IV) silicalites (MFI) and their characterization : A Mössbauer and MAS NMR spectroscopy study. / Fejes, P.; Nagy, János B.; Kovács, Kristóf; Vankó, G.

In: Applied Catalysis A: General, Vol. 145, No. 1-2, 08.10.1996, p. 155-184.

Research output: Contribution to journalArticle

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N2 - The synthesis of tin(IV) (iron, chromium, gallium, indium and titanium) silicalites (MFI) and their characterization by SEM, X-ray diffraction, FTIR, Mössbauer and MAS NMR spectroscopies are reported. In order to obtain 'good quality' crystalline phases the respective metal silicates were prepared first at low pH (pH ca. 2.0) and the sols, containing the substituting metal in homogeneous dispersion at atomic level, were brought to gelation by increasing the pH to about 4.3. These precursor gels were subsequently washed thoroughly by percolation and homogenized in a ball mill. Crystallization was affected at 443 K (170°C) under static conditions. SEM and X-ray diffraction bear witness that the zeolite specimens are completely free of any amorphous phase and are highly crystalline. U.c. volumes decrease with increasing Sn (and Al) contents; an observation which is momentarily at variance with the accepted views. 29Si MAS NMR spectra taken with and without CP prove that defect sites are practically absent. Except titanium silicalite (MFI) the samples show no absorption at around 960 cm-1 in the IR framework region, supporting the view that similar absorptions observed previously also with V, Cr and other elements are due to strained T-O-Si linkages. 119Sn Mössbauer and MAS NMR spectra characterized by I.S. = -0.22 and Q.S. ca. 0 at R.T. and NMR resonance absorption at δ = -700 ppm (relative to SnO2 and tetramethyltin) respectively, prove the tetrahedral coordination of Sn4+ ions in the as synthesized Sn(Al)-ZSM-5 specimens. Standard (non-caring) calcination sets at least part of the substituting element(s) free (clearly observable on MAS NMR spectra and indicated in the 119Sn and 57Fe Mössbauer spectra as well (increase of Q.S. for Sn and both I.S. and Q.S. for Fe)). A caring calcination method which is capable to retain full crystallinity is advanced in this paper. The importance of the retention or partial loss of crystallinity is discussed from the viewpoint of heterogeneous catalysis.

AB - The synthesis of tin(IV) (iron, chromium, gallium, indium and titanium) silicalites (MFI) and their characterization by SEM, X-ray diffraction, FTIR, Mössbauer and MAS NMR spectroscopies are reported. In order to obtain 'good quality' crystalline phases the respective metal silicates were prepared first at low pH (pH ca. 2.0) and the sols, containing the substituting metal in homogeneous dispersion at atomic level, were brought to gelation by increasing the pH to about 4.3. These precursor gels were subsequently washed thoroughly by percolation and homogenized in a ball mill. Crystallization was affected at 443 K (170°C) under static conditions. SEM and X-ray diffraction bear witness that the zeolite specimens are completely free of any amorphous phase and are highly crystalline. U.c. volumes decrease with increasing Sn (and Al) contents; an observation which is momentarily at variance with the accepted views. 29Si MAS NMR spectra taken with and without CP prove that defect sites are practically absent. Except titanium silicalite (MFI) the samples show no absorption at around 960 cm-1 in the IR framework region, supporting the view that similar absorptions observed previously also with V, Cr and other elements are due to strained T-O-Si linkages. 119Sn Mössbauer and MAS NMR spectra characterized by I.S. = -0.22 and Q.S. ca. 0 at R.T. and NMR resonance absorption at δ = -700 ppm (relative to SnO2 and tetramethyltin) respectively, prove the tetrahedral coordination of Sn4+ ions in the as synthesized Sn(Al)-ZSM-5 specimens. Standard (non-caring) calcination sets at least part of the substituting element(s) free (clearly observable on MAS NMR spectra and indicated in the 119Sn and 57Fe Mössbauer spectra as well (increase of Q.S. for Sn and both I.S. and Q.S. for Fe)). A caring calcination method which is capable to retain full crystallinity is advanced in this paper. The importance of the retention or partial loss of crystallinity is discussed from the viewpoint of heterogeneous catalysis.

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