Effect of Rare-Earth (La, Nd, Pr, Y) Doping on the Properties of X-Y-Ce-Zr-O and X-Y-Z-Ce-Zr-O Nanodispersions for GPF Applications

The effect of different rare-earth dopants (Nd, Y, La, Pr) and their combination on the final properties of CeO2-ZrO2 mixed oxide nanodispersions for gasoline particulate filter applications was investigated. The presence of additional two or three dopants improves the thermal stability as they were found to maintain their cubic (c) or pseudo-cubic (t '') phase symmetry after high temperature ageing at 1150 degrees C in contrast to the pure ceria-zirconia reference samples. Doping also improved the surface area and porosity and the thermal stability towards sintering of primary particles. It was observed that La/Pr sample shows initial mesoporosity and the highest thermal stability. A clear link between structural/thermal stability and the oxygen storage performance could be made. The rare-earth doped samples showed improved reduction ability and were reduced in H-2 at temperatures 591-597 degrees C compared to pure ceria-zirconia samples (616-617 degrees C). Furthermore, they were also able to be partially re-oxidized at 50 degrees C whereas the pure ceria-zirconia samples were not. This could be explained by the improved oxygen mobility in the t '' phase for doped materials. Tested samples showed good catalytic performance in the reaction of soot oxidation by TG-DTA. SEM imaging of coated cordierite particulate filters showed that the nanodispersions were coated in a manner that eliminated the small pores in the filter wall and reduced the size of the larger pores. According to literature analysis, these coating characteristics would offer improved performance in relation to filtration efficiency and backpressure.