Redox and chemisorptive properties of ex-chloride and ex-nitrate Rh/Ce0.6Zr0.4O2 catalysts - 1. Effect of low-temperature redox cycling

The influences of low-temperature redox cycling and of the presence of chlo ride on the redox and chemisorptive properties of Rh/Ce0.6Zr0.4O2 were inve stigated by means of volumetric hydrogen chemisorption, temperature-program med 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 inv estigations were also conducted on the pure support. The results demonstrat e that the interaction of Rh/Ce0.6Zr0.4O2 With hydrogen is critically depen dent not only on the presence of chloride but also on the specific treatmen ts 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 chl oride-based preparations for such materials. While some chloride can be rem oved under the low-temperature cycling conditions employed, the extent of t his removal is small, and a lower degree of reduction was attained by the c hloride sample throughout the series of experiments. (C) 2000 Academic Pres s.