The influences of low-temperature redox cycling and of the presence of chloride on the redox and chemisorptive properties of Rh/Ce0.6Zr0.4O2 were investigated by means of volumetric hydrogen chemisorption, temperature-programmed reduction, and temperature-programmed desorption. 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 demonstrate that the interaction of Rh/Ce0.6Zr0.4O2 With hydrogen is critically dependent not only on the presence of chloride but also on the specific treatments applied to the sample. The most important effect of chloride is that it inhibits the extent of vacancy creation at common operating temperatures of working three-way catalysts, thereby highlighting the unsuitability of chloride-based preparations for such materials. While some chloride can be removed under the low-temperature cycling conditions employed, the extent of this removal is small, and a lower degree of reduction was attained by the chloride sample throughout the series of experiments. (C) 2000 Academic Press.