La synthèse de l’ammoniac sur le fer en tant que réaction auto-catalytique

Laboratoire Maurice Letort, Route de Vandœuvre, B.P. n° 104, 54600 Villers-Nancy, France.

Résumé

Le caractère auto-catalytique de la réaction apparaît après chaque modification d’un facteur cinétique. La réponse transitoire du catalyseur comprend une partie rapide et une partie lente. Elles s’expliquent par les adaptations respectivement rapide et lente du film réactionnel et de la teneur superficielle en sites actifs aux nouvelles conditions réactionnelles. On définit une procédure propre à démêler les deux effets et à obtenir la vitesse relative à un nombre constant de sites actifs.

Abstract

The auto-catalytic character of the reaction, previously reported, is shown to exert its influence whenever any of the kinetic factors of the reaction is varied. All the transient responses of the catalyst to a sudden change in its working conditions display fast and slow parts ; they are explained as being respectively due to the adjustment of the chemisorbed reactive film and of the active sites content of the surface to the new working conditions. A procedure is defined in order to disentangle the two effects and to reach the rate which relates to a constant number of active sites despite of the fact that their creation is due to the reaction itself. The possibility for the reaction to do so is conceived as resulting from the conversion of some part of its energy into the energy required to sustain the metal surface out of equilibrium with regard to its defects content.