The catalytic activity of Au-TiO2-In2O3 catalyst in the oxidation of CO in the presence and absence of added water vapour and using different pretreatment conditions was tested and compared with that of a Au-TiO2 sample prepared using a commercial Support used as a reference catalyst. The Au-TiO2In2O3 samples showed less activity than the standard Au-TiO2 sample but could be reused after reaction up to 500 degrees C without loss of activity. The activity of Au-TiO2-In2O3 catalysts for CO oxidation was relatively insensitive to the pretreatment procedures but showed quite distinct light-off curves compared with those of Au-TiO. Differences between the catalytic behaviour of the two Au-supported catalysts indicate differences in the relative ease by which the oxides become dehydroxylated by thermal treatments. Results for Au-TiO2-In2O3 are consistent with a scheme in which at low temperatures (<= 264 degrees C), CO2 formation involves gold sites with participation of hydroxyl groups of the support. Above this temperature, dehydroxylation of the Support leaves the gold component with low activity, and the rate of CO2 formation becomes equivalent to the rate obtained over the support alone. Cooling the samples back to room temperature recovers the initial activity of the gold, confirming that deactivation is completely reversible. Experiments conducted involving deliberate addition of water show that the deactivation caused by an excess of H2O for both Au-TiO2 and Au-TiO2In2O3 is also reversible, and that the extent to which water is retained is quite different for the two catalysts. Reaction mechanisms, taking into account the involvement of H2O, are discussed. (c) 2006 Elsevier Inc. All rights reserved.