The electrochemical response and electrode potential-dependent infrared spectra for CO-adsorbate oxidation on unsupported ruthenium cluster-like material (Ru-x) prepared in two organic solvents: (xylene (Xyl), and 1,2-dichlorobenzene (Dcb)) from tris-ruthenium dodecacarbonyl decomposition, are reported. In spite of a similar particle size (2 nm) of the materials, the interfacial pseudo-capacitance of Ru-x(Xyl) is ca. four times higher than that of Ru-x(Dcb). Wide angle X-ray spectroscopy (WAXS) analysis on Ru-x(Xyl) and Ru-x(Dcb) nanoparticles revealed a high degree of structural disorder on Ru-x(Xyl) (J. Phys. Chem. B 105 (2001) 5238). The surface state of Ru-x(Xyl) and Ru-x(Dcb) used to oxidize CO, to form oxide-like (RuxOy) species, and used to recover the metallic nanoprecursor (under hydrogen annealing) can be inherently attributed to the degree of surface atom disorder. The CO absorption bands recorded on both types of surfaces are linear in nature and have apparently similar behavior to that observed on massive or well-defined ruthenium electrode surfaces. (C) 2003 Elsevier B.V. All rights reserved.