The influences of high-temperature redox cycling and of the presence of chloride on the textural, redox, chemisorptive, and catalytic properties of Rh/Ce0.6Zr0.4O2 were investigated by means of N-2 physisorption, volumetric hydrogen chemisorption, temperature programmed reduction (TPR), temperature programmed desorption, and catalytic activity measurements of the reduction of NO by CO. This was achieved by conducting experiments on two samples of the material prepared from nitrate and chloride precursors. For the purposes of comparison, some parallel investigations were also conducted on the pure support. The results indicate that the precursor used does not affect the extent of vacancy creation upon application of identical high-temperature reduction procedures. However, the high-temperature reduction procedure used does have a detrimental effect on the position of vacancy creation during subsequent TPR profiles after mild reoxidation. Differences in behaviour due to the presence of chloride are detectable after application of such high-temperature reduction/mild reoxidation cycles, mainly in the chemisorption behaviour at low temperature and activity measurements under pseudo-steady-state conditions at 473 K. Significantly, severe ageing under reaction conditions does not eliminate differences in the rates of formation of products during the reduction of NO by CO. (C) 2000 Academic Press.