The deactivation of unconditioned Au/TiO2 catalysts during CO oxidation at different reaction temperatures (30 and 80 degrees C) and in different reaction atmospheres was investigated. Kinetic and in situ IR spectroscopic measurements revealed a close correlation between the exponentially decreasing CO2 formation rate and the COad coverage (decreasing) and carbonate coverage (increasing) during deactivation, whereas transmission electronic microscopy imaging revealed no significant changes in Au particle size. Consequences for the deactivation mechanism are discussed. (C) 2007 Elsevier Inc. All rights reserved.