Precursors of alumina- and silica-supported ruthenium catalysts were prepared by pore volume impregnation of the dehydrated supports with a benzene solution of Ru(acac)(3). The prepared samples were characterized by diffuse reflectance FTIR and TG/DTG-DTA in order to discriminate Ru(acac)(3) which interacts with the support surface. Weight loss, experimentally observed upon thermolysis of parent and supported Ru(acac)(3), was compared with that calculated using the proposed reaction stoichiometry. Conditions for activating silica- and alumina-supported Ru(acac)(3) in an oxidizing atmosphere with complete removal of acetylacetonate ligands from the catalyst precursor are recommended.