Premium
The H/D Exchange and Hydrogenolysis of Butane on an Alumina‐Supported Nickel Catalyst
Author(s) -
Öz Hami,
Gäumann Tino
Publication year - 1992
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19920750319
Subject(s) - chemistry , hydrogenolysis , butane , catalysis , nickel , deuterium , desorption , ethylene , adsorption , alkene , hydrocarbon , product distribution , atmospheric temperature range , organic chemistry , thermodynamics , physics , quantum mechanics
The exchange of butane with deuterium on a nickel/alumina catalyst is studied over a wide range of temperatures (50–230°) and for three hydrocarbon/deuterium ratios. The initial distribution is used to propose a reaction scheme by considering different adsorbed species such as: alkyl‐(α), alkene‐(α, β) and allyl‐(α,β,γ) species, where α, β, and γ are 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 C 4 HD 9 and C 4 D 10 is, thus, explained. The exchange of CH 3 CD 2 CD 2 CH 3 and CD 3 CH 2 CH 2 CD 3 with H 2 and D 2 is also studied, and similar results are obtained as with exchanges of CH 3 CD 2 CH 3 and CD 3 CH 2 CD 3 . 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 2 , the production of propane being favored.