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Reactions of methylcyclopentane hydrogenolysis were performed at 140°C-160°C on two ruthenium catalysts 10%Ru-Al2 O3 - 0.2% RU-Al2 O3 and on two Pt-Ru bimetallic catalysts in order to determine the mechanistic change in hydrogenolysis caused by the interaction between Pt and Ru. The results of this research are explained using the "in-situ" X-ray absorption spectroscopy analysis which pointed out (9) that a Pt-Ru bimetallic phase in the Ru rich phase is present in the catalyst. As in these experimental conditions platinum is inactive, an "activated Pt-Ru clusters ", can explain why the values of the selectivity ratio : 3-methylpentane over n-hexane increase when the number of small metal particles also increase. This result shows that a dilution effect does not occur solely if it occurs.

Des catalyseurs platine-ruthenium supportes sur alumine, prepares par co-impregnation, ont ete etudies in situ en absorption X(EXAFS et XANES) en utilisant le rayonnement synchroton qui est produit dans l'anneau de stockage DCI au LURE (Orsay). Nous montrons que ces catalyseurs sont bien reduits a 400 o C et qu'ils presentent quatre sortes differentes de particules metalliques: des particules de Pt c.f.c., des particules de Ru et des agregats bimetalliques ou allies riches en Pt ou riches en Ru