Hydrogen adsorption on Ru surfaces of Ru/TiO2 catalysts has been investigated in a gas adsorption apparatus at temperatures from 35 to 150 degrees C, H-2 partial pressures from 0.05 to 700 Torr, and adsorption equilibration time at each pressure from 3 to 60 min. Results showed that adsorption of H-2 on the TiO2 support are negligible. TEM measurements suggested that there was no strong metal-support interaction (SMSI) on the synthesized Ru/TiO2 samples to inhibit H-2 adsorption. A transition pressure point of similar to 60 Torr was observed for H-2 adsorption on Ru/TiO2. Most of the strong chemisorption occurs before this transition pressure and weak chemisorption happens thereafter. H-2 adsorption increases with temperatures from 35 to 75 degrees C indicating an activation energy present for H-2 chemisorption on Ru. Above 75 degrees C, the adsorption slightly decreases with further increase of temperature up to 150 degrees C. Monolayer coverage was attained at 75 degrees C for 30 min equilibration time with a H-2 pressure higher than 300 Torr. Monolayer H-2 chemisorption was used to determine Ru metal particle size in Ru/TiO2 systems compared with XRD and TEM analyses. Selected area electron diffraction (SAD) indicated that there was no preferred crystallographic orientation of the TiO2 supported Ru. Therefore, exposed Ru atoms equally contribute from the three low-index planes [(0 0 1), (1 0 0), and (1 1 0)] with the highest atomic density instead of only the (1 0 0) plane for conventional treatments. With this assumption, the average Ru particle size calculated from H-2 chemisorption (4.6 nm) agrees with the TEM measurements (4.1 nm). (c) 2007 Elsevier B.V. All rights reserved.