Ru nanoparticles supported on gamma-Al2O3, prepared by reduction of RuCl3 in ethylene glycol with using microwave irradiation, were thoroughly characterized by ICP-AES, BET, XRD, TEM, XPS and H-2 chemisorption. Structure and chemisorptive properties of the supported colloidal Ru. nanoparticles were compared with those of the Ru/gamma-Al2O3 catalyst prepared by the incipient wetness impregnation method, using the same RuCl3 precursor. Results obtained by volumetric H-2 chemisorption performed at different temperatures 20 200 degrees C, showed that the irreversible H-2 adsorption onto colloidal Ru/gamma-Al2O3 catalyst is a nonactivated process. For this catalyst saturation of the ruthenium surface with hydrogen was achieved already at room temperature. Ruthenium dispersion and particle sizes obtained from H-2 measurements agreed well with the results of TEM and XRD methods. In contrast, activated chemisorption behavior has been observed on traditionally prepared Ru/gamma-Al2O3 catalyst. Even at 100 degrees C, irreversible H-2 uptake was lower then expected as evidenced by the large discrepancies between the mean particle sizes obtained from H-2 chemisorption and TEM. Superior chemisorptive properties of the Ru nanoparticles supported on gamma-Al2O3 are assigned to the higher dispersion of the smaller ruthenium particles and also their weaker interaction with the support. The colloidal catalyst, in contrast to traditionally prepared one, is free of chlorine contamination. Also, contamination of Ru by aluminum ions, possible during the catalyst preparation by conventional impregnation with acidic solution, was avoided. (c) 2007 Elsevier B.V. All rights reserved.