Cu-Ce-Al mixed oxides, which have been shown to be active for soot oxidation, were treated in the presence of sulfur dioxide and water. This catalyst displayed good tolerance to hydrothermal aging at 800 degrees C for 10 h. However, the presence of 1,000 ppm SO2 in wet air led to a distinct loss of activity. The characterizations of XRD, BET, XPS, TPR and FTIR analyses showed that, although no clear sulfate crystallites were observed, the modifications of surface structure and hereby losses in redox and NOx adsorption properties were main factors of deactivation.