fulltext.study @t Gmail

Influence of the parent zeolite structure on chromium speciation and catalytic properties of Cr-zeolite catalysts in the ethylene ammoxidation

Paper ID Volume ID Publish Year Pages File Format Full-Text
40649 45861 2012 13 PDF Available
Title
Influence of the parent zeolite structure on chromium speciation and catalytic properties of Cr-zeolite catalysts in the ethylene ammoxidation
Abstract

Cr-zeolites with MFI, BEA, MOR and FAU structures, prepared by solid-state ion exchange, were characterized and tested in C2H4 ammoxidation to acetonitrile in the temperature range 425–500 °C. Based on characterization results, chromate and/or polychromate species, oxo-cations and small Cr2O3 oxide clusters played a key role in the ammoxidation of ethylene, while agglomerated Cr2O3 and bare Cr cations should be avoided. Cr ions sited in the sodalite and hexagonal cages of NH4+–Y are not accessible to the reactants while available catalytic sites are poorly active. However, the mesopores of the ultra stable Y zeolite (USY) favor the diffusion of reactants to the clustered Cr oxide. The corresponding catalyst is therefore active, but the presence of octahedral Al species is crucial to the ammoxidation. Cr ions in zeolites beta and mordenite led to less active catalysts when compared to ZSM-5. In zeolite beta, the micropores are small; therefore, pronounced interactions between ethylamine intermediate molecules could discourage the acetonitrile formation. In mordenite, agglomerates of Cr2O3 oxide inhibited the accessibility of active sites to the reactants and enhanced the hydrocarbon oxidation. The catalytic performance of Cr ions in ZSM-5 provided from a synergy of different parameters: structural, textural and the acid strength (Si/Al ratio).

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (163 K)Download as PowerPoint slideHighlights► Cr–S solids (S = ZSM-5, mordenite, beta, USY, Y) were tested in C2H4 ammoxidation. ► Cr species with high oxidation states play a key role in the ammoxidation. ► Agglomerated Cr2O3 and bare Cr ions should be avoided during catalyst preparation. ► Catalytic activity is highly affected by the zeolite matrix. ► Interactions between ethylamine intermediate molecules inhibit CH3CN formation.

Keywords
Ammoxidation; Solid-state exchange; Zeolite structure; Thermal analysis; H2-TPR
First Page Preview
Influence of the parent zeolite structure on chromium speciation and catalytic properties of Cr-zeolite catalysts in the ethylene ammoxidation
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us
Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volumes 439–440, 10 October 2012, Pages 88–100
Authors
, , , , , , ,
Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us