The influence of elevated reaction temperatures on the activity, long-time stability, and deactivation behavior of Au/TiO2 catalysts for CO oxidation was studied by kinetic and in situ IR measurements in the temperature range 80-180 degrees C, both in an idealized, H-2-free reaction atmosphere and in a H-2-rich gas mixture. The results are discussed in a molecular picture. Most important for practical applications (PROX reaction), the selectivity for CO oxidation in H-2-rich gas mixtures decreases sharply with increasing temperature, from similar to 60% at 80 degrees C to similar to 15% at 180 degrees C. The increasing tendency for H-2 oxidation is reflected also by a distinctly lower apparent activation energy for CO oxidation in the presence of H2 (18 +/- 3 kJ mol (1)) compared to reaction in a H-2-free reaction mixture (30 +/- 3 kJ mol (1)). In all cases, carbonate formation is observed and proposed to contribute to the deactivation, but with different extents depending on the reaction conditions. (C) 2009 Elsevier Inc. All rights reserved.