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20986.0 [No comment] 30.06.2005 11:47 Released

ID: 20986.0, Fritz-Haber-Institut / Inorganic Chemistry
Reaction Pathways in n-Pentane Conversion Catalyzed by Tungstated Zirconia: Effects of Platinum in the Catalyst and Hydrogen in the Feed
Authors:Kuba, Stefan; Lukinskas, Povilas; Ahmad, Rafat; Jentoft, Friederike C.; Grasselli, Robert K.; Gates, Bruce C.; Knözinger, Helmut
Research Context:1, Acid-base and redox properties of promoted sulfated zirconia
Date of Publication (YYYY-MM-DD):2003
Title of Journal:Journal of Catalysis
Journal Abbrev.:J. Catal.
Start Page:376
End Page:388
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:The catalytic isomerization of n-pentane catalyzed by tungsted zirconia (WZ) was investigated to elucidate the effects of H2 in the feed and platinum in the catalyst. In the reaction catalyzed by WZ with or without platinum, when no H2 was present, a complex reaction network was observed, associated with organic deposits on the catalyst, giving mainly cracked products. The alkane is inferred to be activated in a redox step forming W5+ on the catalyst and unsaturated intermediates that react to form polyalkenylic surface species, which were detected by in-situ UV-visible spectroscopy. Promotion of WZ with platinum dramatically improved the catalytic activity and the isomerization selectivity in n-pentane conversion. The improvement was only marginal in the absence of H2, but it became substantial in the presence of H2, with the conversion increasing from 3 to 55% for the platinum-promoted catalyst, which underwent only little deactivation. The selectivity for isopentane was about 95% at 523 K. The results indicate that the complex reaction network operative with the WZ catalyst is suppressed on the platinum-containing catalysts in the presence of H2. A fast and selective monomolecular isomerization reaction takes over in this case. The adsorbed unsaturated C5 intermediates are rapidly desorbed via hydrogenation on the reduced tungstate surface. This rapid desorption minimizes the formation of higher-molecular-weight organic species such as polyalkenyls that are necessary for the complex reaction path observed with the unpromoted catalyst. The observed side products are interpreted not as cracking products accompanying the acid-catalyzed isomerization reaction but instead as hydrogenolysis products formed directly on the platinum particles.
External Publication Status:published
Document Type:Article
Communicated by:Robert Schlögl
Affiliations:Fritz-Haber-Institut/Inorganic Chemistry/Functional Characterization
External Affiliations:Department of Chemical Engineering, University of Delaware, Newark, Delaware, USA
Department of Chemical Engineering and Materials Science, University of California, Davis, California, USA
Department Chemie, Ludwig-Maximilians-Universität München, Germany
Identifiers:URL: [only for subscriber]
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