Pt and Rh were impregnated by different methods into the washcoat to investigate the differences in Rh oxidation state and catalytic activity of the samples. Both fresh and laboratory aged samples were studied. Clear differences in catalytic activity were noticed between the catalysts with different Pt and Rh addition methods. The best oxidation activity for fresh catalysts was achieved with the catalyst having both Pt and Rh deposited into the Ce-Zr mixed oxide. However, this state was observed to be unstable, and hence, this particular catalyst was dramatically deactivated in air ageing at high temperature. After ageing, the catalyst having both Pt and Rh impregnated lastly into the entire calcined washcoat matrix had the best activity in all three reactions, carbon monoxide and hydrocarbon oxidation and nitrogen oxide reduction. According to XPS studies, Rh was in easily reducible form in all the fresh samples. After ageing, the highest portion of reducible Rh was observed in the sample having also the best catalytic activity. 2004 Elsevier B.V. All rights reserved.