Abstract

Different series of Rh/SiO 2 and Rh/ZrO 2-SiO 2 catalysts prepared by the sol-gel method and the traditional method based on the impregnation of the support with a metal precursor have been obtained. The samples were characterized by measuring the specific surface area by nitrogen adsorption at 77 K, metal surface area by H 2 chemisorption at 298 K, temperature programmed reduction, XRD, TEM and XPS. The catalysts were evaluated in the methylcyclohexane dehydrogenation and the n-butane hydrogenolysis. The results showed that in the catalysts prepared by the sol-gel method, the rhodium particles are strongly interacting with the support. Due to these interactions, a large proportion of the rhodium particles remains buried into the support, therefore they are not reduced and they are unable to take place in catalytic events. Consequently, the surface and catalytic properties of these samples are notably affected. On the contrary, catalysts prepared by the impregnation method, do not present this kind of interactions and their behaviour is the expected one. No significant changes in the turnover number with the particle size in the methylcyclohexane dehydrogenation were detected. This behaviour is in agreement with a structure insensitive reaction.