On the slow uptake of hydrogen by platinized carbon

Boudart, M.; Aldag, A.W.; Vannice, M. A.

doi:10.1016/0021-9517(70)90310-6

Cited by 119 publications

(29 citation statements)

References 3 publications

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“…A mercury manometer and burette which had a reservoir containing mercury were used in conjunction with a manostat to perform kinetic work at constant pressure. The detailed design of the manostat has been discussed elsewhere (Boudart et al, 1970). Another trap at 80°K and a gold trap were placed just before the point where the reactor was connected to the system.…”

Section: Page 904mentioning

confidence: 99%

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

1978

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The areal rate of liquid phase hydrogenation of cyclohexene on supported platinum catalysts does not depend on the nature of the support. Nor does it depend on particle size of the metal. The rate constant is independent of the nature of the solvent when the concentration of hydrogen in it is expressed as its measured or calculated solubility. All observations are compatible with the idea that the measured rate is that of chemisorption of dihydrogen on a metal surface covered with reactive hydrocarbon intermediates. SCOPEThe effect of the dimensions of metallic particles on the catalytic activity of supported metals is of theoretical and practical importance. The present work was undertaken to examine the effect of platinum particle size on the liquid phase hydrogenation of cyclohexene in a rocking slurry reactor. The reaction was studied in a static system at constant hydrogen pressure, normally atmospheric pressure, between 275O and 316OK. As diffusion coefficients in the liquid phase are often two or more orders of magnitude lower than in the vapor phase, diffusional influence can play a substantial role in slurry reactors. It is thus imperative that reactions studied in slurry reactors be examined for diffusional effects and proof be given that observed rates have not been disguised by either intraparticle or interphase mass transport. We set out to obtain true kinetic data devoid of either the influence of transport phenomena or catalyst deactivation during an experimental run.The present study also focused on two important aspects of liquid phase reactions, When heterogeneous catalytic reactions are carried out in the gas phase, ideal gas behavior is ordinarily assumed. However, for kinetics in the liquid phase, as in a slurry or trickle bed reactor, it is necessary first of all to ascertain whether concentrations or activities of dissolved reactants should be used in rate expressions. Second, it is also important to check whether different solvents affect the reaction rate or the rate constant. The literature of catalytic reaction engineering offers few experimental or theoretical guidelines bearing on these two important questions. CONCLUSIONS AND SIGNIFICANCEKinetic data have been obtained for the liquid phase hydrogenation of cyclohexene on supported platinum catalysts in a rocking slurry reactor. First of all, values of the turnover frequency N , defined as molecules reacted per site per second, were obtained on catalysts containing different amounts of platinum of the same dispersion, defined as the ratio of surface metal atoms to total metal atoms. Values of N were found to be identical. As this re- Page 904September, 1978 sult was obtained at two different temperatures, it offers sufficient proof that rates were not masked by artifacts such as the influence of interphase and intraparticle heat and mass transfer, or deactivation and poor contacting of the catalyst by reactants. The main result of this work is that values of N were identical on nine different supported platinum catalysts where the me...

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Section: Page 904mentioning

confidence: 99%

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

1978

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“…The presence of metals that are capable of hydrogen uptake does not necessarily mean that the carbon is inactive. Hydrogen spillover from metals to carbon surfaces is well documented [3,4] and ab initio molecular orbital studies have shown adsorption of hydrogen atoms is exothermic and stable on the graphite basal plane [5]. The spillover of hydrogen involves a transfer of electrons to acceptors within the support; this process not only modifies the chemical nature of the support but can also activate a previously inactive material and/or induce subsequent hydrogen physisorption [6].…”

Section: Introductionmentioning

confidence: 99%

Hydrogen spillover to enhance hydrogen storage—study of the effect of carbon physicochemical properties

Lueking

Yang

2004

Applied Catalysis A: General

302

198

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Hydrogen storage in carbon materials can be increased by hydrogen spillover from a supported catalyst; a systematic investigation of various carbon supports was used to better understand how hydrogen spillover affects hydrogen storage on carbon materials. Secondary spillover experiments effectively eliminated experimental variables associated with primary spillover, evidenced by materials clustering around the carbon type for a variety of supported catalyst-carbon mixtures. Providing a supported catalyst to act as a hydrogen source enhances the overall hydrogen uptake of a carbon material; for example, simple mixing of carbon nanotubes with supported palladium increased the uptake of the carbons by a factor of three. However, the baseline adsorption of the carbon was the predominant factor in the magnitude of the overall hydrogen uptake, even when hydrogen spillover was active. Three observations illustrated that a dynamic steady-state model is needed for predictive capacity of hydrogen spillover.

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“…In a series of studies on benzene hydrogenation over the supported noble metal catalysts, Vannice et al concluded that the use of acidic supports could enhance the rate of hydrogenation [1,2,[4][5][6]. This positive effect was explained by an increased adsorption of benzene with increased acidity of support oxides.…”

Section: Correlation Between Hydrogenation Activity and Smsi Effectmentioning

confidence: 99%

“…Vannices' studies with Pd catalysts in benzene hydrogenation produced a reaction model explaining the enhanced activity over catalysts using more acidic supports [1,2]. This model proposed that benzene adsorbed on acid sites in the metal-oxide interfacial region could react with hydrogen spillover from the metal surface [1][2][3][4][5][6][7]. According to this mechanism, the hydrogenation activity of the supported metal catalyst was determined by three major factors.…”

Section: Introductionmentioning

confidence: 99%

Naphthalene hydrogenation over Pt/TiO2–ZrO2 and the behavior of strong metal–support interaction (SMSI)

Lu¹,

Lin²,

Wang³

2000

Applied Catalysis A: General

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Vapor-phase naphthalene hydrogenation over various supported Pt catalysts was studied in a continuous fixed-bed microreactor. Experimental results indicated that the catalytic activity of the catalyst strongly depended on the nature of the support and the pre-reduction temperature. Reaction order was independent of the support as the reaction was pseudo-first-order with respect to naphthalene in the temperature range studied. By comparing the apparent rate constant over various supported Pt catalysts, Pt supported on TiO 2 -ZrO 2 (1 : 1) reduced at a low temperature showed the highest activity. For higher pre-reduction temperatures, Pt/TiO 2 -ZrO 2 (1 : 1) exhibited the least suppression of H 2 uptake, due to a stabilization effect exerted by ZrO 2 , which prevents the migration of TiO x moieties and the blockage of the Pt surface. However, the apparent depression of the hydrogenation activity of high-temperature reduced Pt/TiO 2 -ZrO 2 (1 : 1) was significantly greater than the suppression of its hydrogen uptake. Furthermore, the decreasing value of the hydrogenation activity relative to the hydrogen uptake demonstrates electron perturbations between the support and the Pt metal.

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On the slow uptake of hydrogen by platinized carbon

Cited by 119 publications

References 3 publications

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

Hydrogen spillover to enhance hydrogen storage—study of the effect of carbon physicochemical properties

Naphthalene hydrogenation over Pt/TiO2–ZrO2 and the behavior of strong metal–support interaction (SMSI)

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