Several graphite-supported Ru-Co and Ru-Ni bimetallic catalysts were comparatively studied by X-ray diffraction (XRD) an CO adsorption microcalorimetry. The correlation of the results thus obtained from these techniques with those on the n-butane hydrogenclysis reaction test, provides useful information about the type and distribution of the surface active sites. The CO adsorption microcalorimetry technique provides, in some cases, information that allows identification and quantification of the surface sites of the metallic nanoparticles. Thus, these data may be used to identify specific catalytic properties (activity and selectivity) in the n-butane/hydrogen test, and how such properties are modified on the different surface sites. Also, comparison with the parent monometallic catalysts allows to envisage, the contribution of each individual metal to the total surface composition or else of the formation of alloys or bimetallic surface clusters. The results so obtained suggest the formation of surface Ru-Co and Ru-Ni alloys on these bimetallic catalysts, their contribution to the surface composition depending on the relative atomic ratio (Ru/M) and on the pre-treatment (reduction) conditions. (C) 2004 Elsevier B.V. All rights reserved.