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Zeolite Cu-ZSM-5: material characteristics and NO decomposition
Kungliga tekniska högskolan, KTH.
Kungliga tekniska högskolan, KTH.
Center for Applied Energy Research, Lexington, KY.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
2000 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 38, no 2-3, p. 287-300Article in journal (Refereed) Published
Abstract [en]

Zeolite ZSM-5 (SiO2/Al2O3 ratio 53:1) ion exchanged with Cu2+ to 0%, 74% and 160% was characterized by X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Infrared (IR) spectroscopy, Electron spectroscopy for chemical analysis (ESCA) and ammonia desorption. A more limited set of data was obtained for Cu-ZSM-5-33, ion exchanged with 0%, 104% and 210% Cu2+ ions. All catalysts lose water below 100°C. More strongly bound water, approximately two molecules per Cu2+ ion, emerge at a higher temperature. This corresponds either to an incomplete hydration shell for zeolite-bound Cu2+ ions or to the decomposition of Cu(OH)2 and simultaneous reactive adsorption of copper ions on the inner surface of the zeolite. The process occurs in the same temperature range, 150-350°C, where XRD reveals rearrangements in the H-form of the catalyst. Reactions between the exchangeable cations and the zeolite appear critical for lattice changes and possibly the formation and dispersion of catalytically active centers at these temperatures. Dehydroxylation and water desorption are observed between 350°C and 450°C for H-ZSM-5. This temperature range overlaps with the light-off temperature for direct NO decomposition over Cu-ZSM-5. This coincidence can be rationalized in terms of two effects of enhanced ionic mobility and dynamics of the zeolitic framework. ESCA shows that partial reduction, cupric to cuprous, occurs as a result of annealing in the same temperature range. It has been suggested that NO-derived surface intermediates act as site blockers for the direct decomposition below the light-off temperature until destabilized by lattice movements. The lower stability and thus higher mobility of low SiO2/Al2O3 ratio ZSM-5 zeolites would then rationalize an advantage of these materials as supports in catalysts for direct NO decomposition.

Place, publisher, year, edition, pages
2000. Vol. 38, no 2-3, p. 287-300
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Fysik
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URN: urn:nbn:se:ltu:diva-8358DOI: 10.1016/S1387-1811(00)00148-7ISI: 000089323800017Scopus ID: 2-s2.0-0034253285Local ID: 6dd7a4c0-f1c2-11db-bb1b-000ea68e967bOAI: oai:DiVA.org:ltu-8358DiVA, id: diva2:981250
Note
Validerad; 2000; 20070423 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved

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