Mechanisms of hydrogenolysis and isomerization of hydrocarbons on metals. VIII. Isomerization of carbon-13 labeled pentanes on a 10% platinum-aluminum oxide catalyst

Garin, F.; Gault, F.G.

doi:10.1021/ja00849a004

Cited by 139 publications

(30 citation statements)

References 3 publications

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“…The side products contained mainly ethane/propane and methane/butanes in equimolar amounts, respectively. These products are typical for hydrogenolysis of pentane as observed with numerous oxide-supported platinum catalysts Pt/MO x (M = Al (43)(44)(45)(46), Si (47,48), Mg (49), Ti (50), Ce/Ti (51)). We therefore propose that the ethane/propane and the methane/butane side products are formed directly on platinum particles without the involvement of the tungsten species.…”

Section: N-pentane Conversion Catalyzed By Ptwz In the Presence Of Hmentioning

confidence: 71%

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

Kuba

Lukinskas

Ahmad

et al. 2003

Journal of Catalysis

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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 W 5+ on the catalyst and unsaturated intermediates that react to form polyalkenylic surface species, which were detected by in-situ UVvisible 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 highermolecular-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.

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Section: N-pentane Conversion Catalyzed By Ptwz In the Presence Of Hmentioning

confidence: 71%

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

Kuba

Lukinskas

Ahmad

et al. 2003

Journal of Catalysis

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“…This surprising result, in contrast to what is generally reported in literature for Pt/silica-alumina catalysts, was accounted for by using the complete form of the Langmuir rate expression. 5,31,32 The new constant, K PD , represents the product of the equilibrium constants for dehydrogenation and protonation elementary steps. Hence, the distinction between protonation and chemisorption as RDS is not critical in the present model.…”

Section: Modelmentioning

confidence: 99%

Hydrocracking of Fischer‐Tropsch waxes: Kinetic modeling via LHHW approach

et al. 2011

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A lumped kinetic model to describe the hydrocracking of complex mixtures of paraffins, such as Fischer-Tropsch waxes, has been developed. A Langmuir-HinshelwoodHougen-Watson approach has been followed, accounting for physisorption by means of the Langmuir isotherm. Finally, a complete form of the rate expression is used, thus introducing the equilibrium constants for dehydrogenation and protonation elementary steps. To minimize the number of model parameters, the kinetic and thermodynamic constants are defined as functions of the chain length. Vapor-liquid equilibrium is calculated along the reactor, and the hydrocarbons concentrations are described by means of fugacity. The model provides quite a good fitting of experimental results and is able to predict the effects of the operating conditions (temperature, pressure, H 2 / wax ratio, and WHSV). Outstandingly, the estimated values and trends of the kinetic and thermodynamic constants (activation energies, Langmuir adsorption constants, etc.) are in line with their physical meaning.

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“…One involving an α , α , β triadsorbed precursor, Anderson -Avery mechanism [5] , and the Garin -Gault mechanism involving a metallacyclobutane intermediate [26] , Scheme 17.1 .…”

Section: Infl Uence Of the Mean Metallic Particle Sizes In Catalytic mentioning

confidence: 99%

“…The global equation is: For example, a value of − 3.5 for the order versus hydrogen, found for cyclic type isomerization of pentane and hexanes [12,26,52] would mean that the reactive species is obtained by rupturing at least seven carbon -hydrogen bonds. Since it is diffi cult to imagine fi rst that species such as [C 5 H 5 ] ads or [C 6 H 7 ] ads could react further to give isomer products and secondly to fi nd a parallel with any surface organometallic complex [53] , another approach has been taken.…”

Section: Kinetic Modelsmentioning

confidence: 99%