Corrélation entre l’activité catalytique d’un film métallique et la nature des radicaux chimisorbés. I. — Étude du système hétérogène méthane, hydrogène et molybdène

Coekelbergs, R.; Delaunois, Y.; Frennet, Alfred; Liénard, Georges

doi:10.1051/jcp/1964611167

Cited by 8 publications

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“…These results reinforced the mechanism already proposed in Reaction 1 [12]; and they concluded that the knowledge of the surface states resulting from the reactions of the gases with the catalyst is essential in order to predict the catalytic activity [17].…”

Section: Exchange Reactions: C-h Bond Ruptures Are Involvedsupporting

confidence: 82%

“…[12] and [13] Coekelbergs et al found some discrepancies in their interpretations compared to the ones of Kemball. In fact Kemball interpreted his results by a adsorptiondesorption mechanism where the slow step was desorption [14], and all his work was performed under static conditions which give much more complicated results even at initial conditions because the equilibrium is not reached.…”

Section: Exchange Reactions: C-h Bond Ruptures Are Involvedmentioning

confidence: 90%

“…About 10 years after this pioneer work done by the groups of Kemball and of Turkevich, another approach was taken by Coekelbergs et al [12] by using carbon-14. They focussed their attention on the adsorbed species.…”

Section: Exchange Reactions: C-h Bond Ruptures Are Involvedmentioning

confidence: 99%

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Site requirements in the kinetics of alkane transformations catalysed by metals

Garin

2006

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Hydrogen pressure is often found to cause an inhibiting effect on the kinetics of alkane reactions on metal surfaces. The most common interpretation of such results is focussed on the degree of dehydrogenation of the active surface intermediate following a dissociative mechanism. A series of arguments will be given in favour of an associative mechanism in which the hydrocarbon reacts with an adsorbed hydrogen atom. In this mechanism, the adsorption site or ''landing site'' is composed of a chemisorbed hydrogen atom associated with an ensemble of ''Z'' potential sites. These sites are associated with the hydrogen chemisorption site. The validity of H 2 adsorption to determine the metallic dispersion will be also discussed.

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Section: Exchange Reactions: C-h Bond Ruptures Are Involvedsupporting

confidence: 82%

Section: Exchange Reactions: C-h Bond Ruptures Are Involvedmentioning

confidence: 90%

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Site requirements in the kinetics of alkane transformations catalysed by metals

Garin

2006

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Skeletal rearrangements of hydrocarbons on metals

Gault

Amir‐Ebrahimi

Garin

et al. 1979

Bulletin des Soc Chimique

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SUMMARYThis paper is a report of some new investigations in the field of skeletalThe kinetics of isomerization are considered first. While in the case of rearrangements on metals.pentanes and hexanes the orders vs hydrogen of the various elementary steps are negative, they are positive in the case of heptanes. However it is shown by using 13C-labeled molecules that no scrambling of the label occurs during the isomerization process. The rate-determining step then is in all cases the skeletal rearrangement of a highly dehydrogenated species. In order to account for the change of orders vs hydrogen, the multisite model proposed by Frennet and coworkers (J. Catal 53, 150, 1978) is adapted to skeletal isomerization.pentane and in methylcyclopentane hydrogenolysis are considered next. It is shown that both bond-shift and cyclic-type isomerizations take place one the same sites, presumably the edge atoms of the crystallites. Two limitinq sizes are defined : one at 10 A below which bond-shift isomerization is converted into non-selective cyclic type isomerization. The second one at 25 A , below which the hydrogenolysis of methylcyclopentane changes from selective to nonselective. Possible crystallographic models are discussed, which could explain the results. None of them is satisfactory and it is suggested that the changes of mechanisms are due to changes in the electronic structure of the metal particles. This view is corroborated by a comparative study of the isomerization of 13C-labeled hexanes on various group VIII metals.In the last section, one of the bond-shift mechanisms and the two cyclic mechanisms, selective and non selective, are described in details. The bondshift isomerization is best described as a reversible dismutation of metallocyclobutane into metallocarbene of internal C-C bonds in isopentane and n-pentane. On the other hand, the non-selective and selective cyclic mechanisms for iso~erization are represented as dicarbene and dicarbyne recombinations respectively. The importance of metallocarbenes and metallocarbynes for other types of skeletal rearrangement such as hydroqenolysis is also emphasized and a classification is given for the contact reactions of hydrocarbons on metal surfaces.

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Metal Catalysed Skeletal Reactions of Hydrocarbons

Maire

Garin

1984

Advances in Comparative and Environmental Physiology

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Corrélation entre l’activité catalytique d’un film métallique et la nature des radicaux chimisorbés. I. — Étude du système hétérogène méthane, hydrogène et molybdène

Cited by 8 publications

References 0 publications

Site requirements in the kinetics of alkane transformations catalysed by metals

Site requirements in the kinetics of alkane transformations catalysed by metals

Skeletal rearrangements of hydrocarbons on metals

Metal Catalysed Skeletal Reactions of Hydrocarbons

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