Exchange reactions of hydrocarbons on silica-supported Rh–Pt bimetallic catalysts

Oliver, James; Kemball, C.; Brown, R. D.; Jamieson, Edward W.

doi:10.1039/f19858101871

Cited by 13 publications

(8 citation statements)

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“…3,3-Dimethylplatinacyclobutane is an example of the type of metallacycles that may result from the α,γ-coordination of hydrocarbon moieties believed to occur during the catalytic hydrogenolysis and isomerization of alkanes . The data presented in this paper strongly suggest the formation of a α,γ-diadsorbed species on Pt(111) in the case of neopentyl moieties on Pt(111), though this reaction seems to compete with the production of neopentylidene species.…”

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confidence: 77%

Change in Reaction Pathway Induced by Deuteration: Thermal Decomposition of Neopentyl Groups on Pt(111) Surfaces

1997

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confidence: 77%

Change in Reaction Pathway Induced by Deuteration: Thermal Decomposition of Neopentyl Groups on Pt(111) Surfaces

1997

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“…Especially D,, has grown at the expense of the D,-D, species, showing the reduced importance of back-exchange. It means that a catalyst with a higher activity deuterates faster, but back-exchange tends to reduce the degree of deuteration of the deuterated fraction, as has been shown for the initial exchange distributions with butane/D, and propane/D, obtained on the Pd, Rh, and Pt catalysts [4] [5] [7] [22] [26].…”

Section: The Isobaric Multiplets O F a Representative Sample Ofpartmentioning

confidence: 99%

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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“…that the 1,2-process may involve aapp-adsorbed species and the minor 1,3-process aayy-species. Rhodium shows high activity for the multiple exchange of methane and of methyl groups attached to quaternary carbon atoms (Kemball 1959;Oliver et al 1985 ;Brown & Kemball 1989). These reactions involve the reversible formation of aa-adsorbed or carbene intermediates.…”

Section: Temperatures Up To 455 Kmentioning

confidence: 99%

“…Thus, the 60% increase in activity from catalyst 500 to catalyst 520 for the ring-opening reaction with cyclopentane could be attributed to the difference in the dispersions of 0.86 and 0.62 respectively. The high activity of catalyst 520 for the hydrogenolysis of cyclopentane may also be related to its effectiveness for the multiple exchange of methane (Oliver et al 1985), and for the higher selectivity than rhod multiple exchange of 2,2-dimethylpropane (Brown et al 1985). The pattern of activity across the series for the reaction of 2-methylbutane differs from the others in showing a relatively marked change in activity between catalysts with 40 % or more of rhodium and those with 20% or less.…”

Section: Temperatures Above 455 Kmentioning

confidence: 99%

Hydrogenolysis and related reactions of hydrocarbons (C ₃ to C ₅ ) on silica-supported Rh-Pt bimetallic catalysts

1990

Proc. R. Soc. Lond. A

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The reactions with hydrogen of propane, butane, 2-methylpropane, pentane, 2-methylbutane, 2, 2-dimethylpropane and cyclopentane have been studied in a static reactor using a series of highly dispersed rhodium-platinum catalysts supported on high-area silica. The main reaction over all catalysts was hydrogenolysis involving the breaking of a single carbon-carbon bond. Most of the compounds reacted at similar rates over platinum with activation energies in the range 132-144 kJ mol -1 . With rhodium, rates varied with hydrocarbon structure by factors of more than 10 2 . The selectivities for the formation of the various products showed that the relative rates of breaking different carbon-carbon bonds over rhodium were S-S > P-S > S-T > P-T > P-Q (P = primary, Q = quaternary, S = secondary and T = tertiary). At temperatures above 455 K, there was evidence of a change of rate-determining step over rhodium with the overall reaction becoming controlled by the rate of desorption of methane. Probable mechanisms over platinum and rhodium are discussed. Rhodium was more active than platinum by factors of about 200 for branched hydrocarbons and of 10 3 or more for straight-chain compounds. Patterns of activity with metal composition are interpreted in terms of active sites consisting of ensembles of about six metal atoms. But an alternative description of the active site as a single metal atom with properties influenced by a number of nearest neighbours cannot be excluded.

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Exchange reactions of hydrocarbons on silica-supported Rh–Pt bimetallic catalysts

Cited by 13 publications

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Change in Reaction Pathway Induced by Deuteration: Thermal Decomposition of Neopentyl Groups on Pt(111) Surfaces

Change in Reaction Pathway Induced by Deuteration: Thermal Decomposition of Neopentyl Groups on Pt(111) Surfaces

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

Hydrogenolysis and related reactions of hydrocarbons (C ₃ to C ₅ ) on silica-supported Rh-Pt bimetallic catalysts

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Exchange reactions of hydrocarbons on silica-supported Rh–Pt bimetallic catalysts

Cited by 13 publications

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Change in Reaction Pathway Induced by Deuteration: Thermal Decomposition of Neopentyl Groups on Pt(111) Surfaces

Change in Reaction Pathway Induced by Deuteration: Thermal Decomposition of Neopentyl Groups on Pt(111) Surfaces

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

Hydrogenolysis and related reactions of hydrocarbons (C 3 to C 5 ) on silica-supported Rh-Pt bimetallic catalysts

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Hydrogenolysis and related reactions of hydrocarbons (C ₃ to C ₅ ) on silica-supported Rh-Pt bimetallic catalysts