Two rhodium catalysts supported on alumina (metal loading 1 and 3 wt.%) were comparatively studied by H-2 and CO adsorption microcalorimetry and by infrared spectroscopy of the chemisorbed CO. The correlation of the results obtained from these two techniques with the n-butane hydrogenolysis reaction test provides useful information about the type and distribution of the surface active sites. The energetic distribution of surface sites has been shown to depend slightly on the metal loading and it can be modified by the pretreatment conditions. The obtained results also reveal the presence of partially reduced Rh atoms stabilized by Cl ions remaining from the precursor. On the other hand, the increased density on Rh (111) planes on the sample with 3 wt.% Rh treated with water, detected from CO adsorption experiments, can be related with enhanced both activity for the hydrogenolysis reaction and selectivity towards ethane. (C) 2004 Elsevier B.V. All rights reserved.