Effect of Specific Surface Area of Ceria-Zirconia Solid Solutions on Their Oxygen Storage Capacity

Abstract

The oxygen storage capacity (OSC) of a ceria-zirconia(CeO₂-ZrO₂) solid solution containing 50 mol% ZrO₂ is approximately 400 μmol-O₂/g, which corresponds to approximately 50% of the theoretical OSC limit calculated from the valence change of the Ce ion. There are two possible explanations for the OSC suppression of approximately 50% of the theoretical OSC limit. The first mechanism is based on the thermodynamic reaction equilibrium; the second one is based on chemical kinetics. To clarify the reason for the suppression, the effect of the specific surface area of CeO₂-ZrO₂ solid solutions was estimated by measuring the OSC of CeO₂-ZrO₂ solid solutions with 3 levels of specific surface area. OSC was independent of the specific surface area of the CeO₂-ZrO₂ solid solutions in the composition range ≥60 mol% ZrO₂. The amount of bulk oxygen, which is released from inside the crystal lattice, could be estimated to be constant even though the specific surface area of the material changed in the composition range ≤50 mol% ZrO₂. Therefore, the mechanism of the OSC suppression was the thermodynamic equilibrium of the redox reaction of CeO₂-ZrO₂ solid solutions.