A theoretical model of the ethane/deuterium exchange reaction catalysed by platinum. The nature of the αβ process

Hegarty, Bernard F.; Rooney, John J.

doi:10.1039/f19898501861

Cited by 15 publications

(2 citation statements)

References 3 publications

(3 reference statements)

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“…The measured distribution is similar to the pattern obtained on a Pt/silica catalyst [5] [24]. It is often observed and has been subject to a theoretical treatment assuming two different adsorption sites on the catalyst [25], a model that has been recently strongly criticized [26].…”

Section: The Isobaric Multiplets O F a Representative Sample Ofpartsupporting

confidence: 68%

The H/D Exchange and Hydrogenolysis of Butane on an Alumina‐Supported Nickel Catalyst

Öz

Gäumann

1992

Helvetica Chimica Acta

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The exchange of butane with deuterium on a nickel/alumina catalyst is studied over a wide range of temperatures (SO-230°) and for three hydrocarbon/deuterium ratios. The initial distribution is used to propose a reaction scheme by considering different adsorbed species such as: alkyl-(cc), alkene-(a,B) and allyl-(cc,p,y) species, where a, 8, and yare different C-atoms. It is assumed that each adsorbed species can either desorb directly while exchanging one, two, and three H-atoms or undergo multiple exchange before desorption. It is shown that by reducing the activity of the catalyst a back-exchange of the fully deuterated species sets in a lower temperature; a systematic deviation of all model calculations for the estimation of the concentrations of the C4HD9 and C4DI0 is, thus, explained. The exchange of CH3CD2CD,CH, and CD,CH2CH2CD3 with H, and Dz is also studied, and similar results are obtained as with exchanges of CH,CD2CH3 and CD3CH2CD3. With the help of very-high-resolution mass spectra, it is shown that the initial degree of deuteration, i.e. the degree of deuteration after one adsorption step, is 84% for the methylene and 57% for the methyl group respectively. The hydrogenolysis reactions of butane is studied in the same system between 180" and 230". A wide range of conversion is covered, and the product distributions are fitted to kinetic equations in order to obtain the initial rate constants. On the nickel/alumina catalyst one or several C-C bonds are broken before the desorption of the species. Under the conditions used in these experiments, the surface cracking is the rate-limiting step. An isotope effect is observed for the decomposition in D,, the production of propane being favored.Introduction. -Exchange Reactions. The D exchange in saturated hydrocarbons has been intensively studied on different type of catalysts in order to understand the mechanism of hydrocarbon reactions on metals. Studies involving exchange between D, and butane has been described in several publications [ 1-81, but only one author worked with Ni catalyst [9].In [lo], we have modified a model proposed earlier for C, hydrocarbons/D, exchange on the same catalyst [l I]. The study of the propane/D, exchange could be explained by assuming mono-and triadsorbed species. However, at low temperature and by studying two labeled propanes, CH,CD,CH, and CD,CH,CD,, with H, or D,, the presence of a diadsorbed species had also to be taken into consideration. The number of parameters needed to quantify the exchange reaction was thus five, an unreasonable high number. To test the ideas developed earlier, we extended these studies to the next member of saturated alkanes, butane.Hydrogenolysis Reactions. The hydrogenolysis reactions of butane were studied on Ni films [ 121, on 10% Ni/silica gel in integral packed or fluidized bed reactors [ 131 [14], on Ni powder [15], Ni-Cu over silica-supported catalyst [16], and 5 wt.-% Ni on dealuminated silica-alumina catalyst [17]. Nazimek and Ryczkowski [18] have studied the same reaction to show the...

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Section: The Isobaric Multiplets O F a Representative Sample Ofpartsupporting

confidence: 68%

The H/D Exchange and Hydrogenolysis of Butane on an Alumina‐Supported Nickel Catalyst

Öz

Gäumann

1992

Helvetica Chimica Acta

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“…An important feature for a proper test reaction is that it should be metal-catalyzed only. The isotopic exchange of hydrogen with deuterium in hydrocarbons (H/D exchange) is a typical metal-catalyzed reaction [13][14][15][16]. During H/D exchange, hydrogen atoms of a hydrocarbon are replaced by deuterium atoms.…”

Section: Introductionmentioning

confidence: 99%

Support-induced compensation effects in H/D exchange of cyclopentane

Oudenhuijzen¹,

Bokhoven²,

Koningsberger³

2003

Journal of Catalysis

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The exchange of hydrogen for deuterium (H/D exchange) in cyclopentane was measured for Pt catalysts with supports of various acidity. With an earlier developed Monte-Carlo model the contributions of the various possible intermediates in the H/D exchange can directly be measured. It was shown that the activity and the selectivity in the H/D exchange over the supported Pt catalysts strongly depend on the support acid/base properties. The activities of the various catalysts show a compensation effect. The compensation effect can directly be correlated to the contribution of the various exchange mechanisms, which proceed via different intermediates. The contribution of each intermediate depends on the electronic properties of the Pt particles, which in turn depend on the support acidity. This shows that the compensation effect is caused by support-induced changes in the adsorption modes of cyclopentane.

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Heterogeneous palladium‐catalyzed exchange labelling of representative organic compounds with tritium gas

Williams

Than

Rabbani

et al. 1995

Labelled Comp Radiopharmac

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SummaryA range of organic substrates was successfully exchanged with tritium gas using NaI3Hq-reduced palladium oxide or chloride as catalyst. Exchange conditions involved a reaction temperature of 100 OC, a reaction time of 3 days, and products were analyzed by radio-gas chromatography and 3H NMR spectroscopy. Both aromatic and aliphatic compounds underwent exchange, 18 of the 22 substrates incorporated >35% of the available tritium, and most products showed high radiochemical purity. 3H NMR analyses showed that both alkanes and the alkyl chains of alkylbenzenes were rapidly and evenly labelled. Some aromatic compounds showed general ring exchange while others showed high specificity.These results for bulk palladium catalyst are strikingly different from those obtained with bulk platinum and supported palladium catalysts. The results are discussed in terms of currently accepted mechanisms of heterogeneous metal catalyzed hydrogen isotope exchange reactions.

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A theoretical model of the ethane/deuterium exchange reaction catalysed by platinum. The nature of the αβ process

Cited by 15 publications

References 3 publications

The H/D Exchange and Hydrogenolysis of Butane on an Alumina‐Supported Nickel Catalyst

The H/D Exchange and Hydrogenolysis of Butane on an Alumina‐Supported Nickel Catalyst

Support-induced compensation effects in H/D exchange of cyclopentane

Heterogeneous palladium‐catalyzed exchange labelling of representative organic compounds with tritium gas

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