Oxygen adsorption overPt/TiO2 surfaces were investigated as a function of metal loading. Oxygen adsorption over pure TiO2 was molecular at all pressure ranges investigated. On the other hand, differential heats of adsorption measured by adsorption calorimetry indicated that oxygen adsorption was dissociative over Pt/TiO2 surfaces until the Pt surface was saturated with oxygen. The saturation coverage of atomic oxygen on Pt was determined as approximately one from adsorption calorimetry. The initial heat of oxygen adsorption was determined as similar to375 kJ/mol over 0.5 wt.% Pt/TiO2. The differential heats of oxygen adsorption at coverages less than one monolayer of Pt surface was similar to200 kJ/mol consistent with the oxygen adsorption heats over Pt single crystals reported in the literature. As the pressure increased after the saturation of Pt surface, oxygen adsorption continued in a manner similar to oxygen adsorption over pure TiO2. Isosteric heats of oxygen adsorption over pure and Pt/TiO2 samples at coverages >5 mumol/g catalyst were determined to be around 10 kJ/mol. The amounts of oxygen adsorption over Pt/TiO2 surfaces depended strongly on the pretreatment conditions. Most favorable oxygen adsorption was observed over calcined/reduced samples. (C) 2003 Elsevier B.V. All rights reserved.