Oxygen storage and redox properties of Nb-doped ZrO2-CeO2-Y2O3 solid solutions for three-way automobile exhaust catalytic converters

- Nb-doping enhances oxygen storage capacity of zirconia-ceria-yttria solutions.
- Enhancement of the oxygen storage performance by Nb-doping is only temporary.
- Degradation is caused by segregation of Nb under oxidizing conditions.
- Segregated Nb species re-disperse into the solid solution by Pt impregnation.
- Pt-impregnation stabilizes performance of Nb-containing oxygen storage component.

It is shown that Nb-doped ZrO2-CeO2-Y2O3 solid solution (Nb-ZrCeYO) samples have enhanced oxygen storage (OS) capacity compared with Nb-free solid solutions. However, after several days of exposure to ambient air, the OS behavior of the Nb-doped samples shows significant degradation. This degradation is slowed for samples stored in evacuated glass tubes. It is argued that Nb segregation or increase in the extent of this segregation to the surface upon extended exposure to ambient oxygen is the cause of the degradation. After impregnation with Pt, the enhancement of the OS capacity of Nb-doped oxygen storage component (OSC) relative to the Nb-free OSC is restored. The electrons supplied by metallic Pt mimic reducing conditions, which are known to result in migration of Nb away from the surface and re-dispersion into the bulk solid solution. Nb-doped samples impregnated with Pt show stable, time-independent OS performance.

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