par Liénard, Georges 
;Degols, L.
Référence Bulletin des Sociétés chimiques belges, 99, 10, page (817-831)
Publication Publié, 1990
;Degols, L.Référence Bulletin des Sociétés chimiques belges, 99, 10, page (817-831)
Publication Publié, 1990
Article révisé par les pairs
| Résumé : | Reaction of ethane over rhodium model catalyst is studied using a method combining non steady‐state transient effect and labelling with a large excess of deuterium. Relaxation of the catalytic system after an ethane pressure jump as well as rates at steady‐state activity are measured, at 50°C, in a deuterium pressure range from 10−3 to 10−1 Torr. The method differentiates the part of ethane adsorption rate (Rac) that produce carbonaceous species, intermediates for hydrogenolysis. The important variations of the rates of ethane adsorption Rac and of hydrogenolysis with hydrogen pressure and temperature are analyzed in the frame of the ensemble model developped preciously. Both rates are regulated by the demanding character of finding an ensemble of free sites but a larger ensemble is required for hydrogenolysis than for ethane adsorption. In using the formalism of the ensemble model, activation energies are calculated as low as 17 kJ/mole for adsorption and 8kJ/mole for hydrogenolysis. The temperature factors experimentaly measured are strongly depending on the hydrogen coverage θH. It is concluded that all the steps in the reaction scheme, except the desorption one, are reversible but in a more or less degree, depending on the hydrogen coverage. Thus the ethane adsorption step may vary, according to the experimental conditions (p,T) from complete irreversibility (hydrogenolysis formation), at low θH, to nearly complete reversibility, for high θH coverage values. In this case ethane adsorption still proceeds without hydrogenolysis. Copyright © 1990 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim |
