Effects of redox treatments on the structural composition of a ceria-zirconia oxide for application in the three-way catalysis

The influence of calcination and redox cycles on the structural modification and redox properties of a ceria-zirconia mixed oxide of nominal composition Ce0.6Zr0.4O2 were investigated by XRD and Rietveld refinement, by BET measurement, TPR and OSC analyses. The material is characterized by high total OSC and retains this property after several redox and calcination cycles up to 1273 K, despite the loss of porosity and the decrease of surface area. The Rietveld analysis of the diffractograms allowed to establish that at least two solid solutions are present in the as-prepared sample: a cubic phase, space group Fm-3m, richer in cerium compared to the nominal composition, a tetragonal phase (t?) richer in zirconium. The first redox treatment modifies the composition towards two different solid solutions with composition closer to the nominal one: a cubic Ce0.65Zr0.35O2 and a tetragonal (t?) Ce0.47Zr0.53O2. No changes are noticed after four further redox cycles, while the successive calcination at 1273 K gives rise to a second cubic phase richer in cerium and to another tetragonal phase richer in zirconium. Noteworthy a further redox cycle reorganizes the sample to a similar situation as before the calcination treatment and this configuration is maintained for four redox cycles. This alternance is restored after calcination and successive four redox cycles. The total OSC measured after the above treatments is high and increases after the successive cycles. © 2002 Elsevier Science B.V. All rights reserved.