Treatment under H-2 at 300 degrees C of Ru(COD)(COT) dispersed on silica yields 2 nm ruthenium nanoparticles, [Ru-p/SiO2], according to EXAFS, HRTEM and XPS, H-2 adsorption measurements on [Ru-p/SiO2] in the absence of O-2 show that Ru particles adsorb Lip to ca. 2H per surface ruthenium atoms (2H/Ru-s) oil various samples; this technique can therefore be used to measure the dispersion of Ru particles. In contrast, O-2 adsorption on [Ru-p/SiO2] leads to a partial oxidation of the bulk at 25 degrees C, to RuO2 at 200 degrees C and to sintering upon further reduction under H-2, Showing that O-2 adsorption cannot be used to measure the dispersion of Ru particles. (C) 2008 Published by Elsevier Inc.