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In situ Mössbauer study of framework substituted (Fe)ZSM-5 zeolites

✍ Scribed by K. Lázár; G. Borbély; H. Beyer

Publisher
Elsevier Science
Year
1991
Tongue
English
Weight
803 KB
Volume
11
Category
Article
ISSN
0144-2449

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✦ Synopsis

The coordination states, stability, and reducibility of isomorphically substituted framework Fe(lll) were studied in ZSM-5 zeolites (Si/Fe = 22) by in situ M6ssbauer spectroscopy. Supplementary methods as X-ray diffraction and temperature-programmed reduction were used as well, and the catalytic activity of (Fe)ZSM-5 was tested in CO hydrogenation. The effects of exchange of charge neutralizing protons for Li + were also studied. The measurements revealed that the symmetry of coordination of the framework Fe(lll) depends considerably on the nature of charge compensation. It can be suggested that Br6nsted acidic bridged hydrogen induces greater asymmetry around the framework Fe(lll) than that generated by cationic (e.g., Li + H30 +, or PrNH~) compensation. The framework Fe(lll) withstands hydrogen reduction and CO + H2 treatment at 570 K, but a part of these substituted ions can be reduced to Fe 2+ state at 670 K. Li + ion exchange decreases the reducibility of the framework Fe(lll).

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Fe and B substitution in ZSM-5 zeolites:
Fe and B substitution in ZSM-5 zeolites: A quantum-mechanical study
✍ A. Chatterjee; A.K. Chandra 📂 Article 📅 1997 🏛 Elsevier Science 🌐 English ⚖ 560 KB

Density functional theory has been used to study isomorphous substitution of Fe and B for Si in orthorhombic MFI type zeolite ZSM-5. Calculations were performed on monomer [TV], dimer [(OH),-Si-0-T-(OH),] and pentamer T(OSiO,H,), cluster models where T = Fe or B. It has been experimentally observed