University of Alicante

Ce_0.5Pr_0.5O₂

particles size smaller than 9 nm and specific surface areas higher than 90 m²/g. The method used allows obtaining 7 nm particles with 125 m²/g surface area.

1. The cerium and praseodymium precursors are dissolved in water.

2. An emulsion is prepared with the previous water solution.

3. Another alkali emulsion is prepared.

4. Both emulsions are mixed.

5. The solid obtained is separated by centrifugation.

6. The solid is calcined at T > 400ºC.

Figure 1 shows the soot conversion profiles obtained with the novel ceria-praseodymia nanoparticles under a diesel exhaust simulated gas mixture (500 ppm NO + 5% O₂ en N₂; 30000 h-1). Reference curves obtained with a commercial 1% Pt/alumina catalyst, with a ceria-praseodymia prepared by a conventional precipitation procedure and without catalyst. All soot:catalyst mixtures used simulate the loose contact attained in real conditions.

Figure 2 shows the relationship between soot combustion capacity and catalyst particle sizes/Surface area (under the experimental conditions of Figure 1) for ceria-based mixed oxides with zirconium of praseodymium. All catalysts were calcined at 500 ºC, otherwise indicated.

In order to provide a wider comparison, Table 1 compiles the T50% parameter, which is the temperature required for 50% soot conversion in the experimental conditions of Figures 1 and 2, for catalysts of very different formulation.

Tabla 1. Comparison of diesel soot combustion catalyst tested in realistic experimental conditions (loose soot-catalyst contact and NOx+O₂ gas mixture):

Doped ceria catalysts either with zirconium or praseodymium show high activity, but the platinum catalysts performance is on only overcome by the ceria-praseodymia catalysts prepared in the current invention by the microemulsion method. The high activity of these ceria-praseodymia catalysts is related to: (i) the intrinsic high catalytic activity of ceria-praseodymia mixed oxides, which relies on the high production of active oxygen species and (ii) the small particle size, which allows the transfer of such active oxygen species from catalyst to soot particles. This is evidenced on Figure 2, where the T50% temperature is plotted against the catalyst particle size for two sets of ceria-based catalysts. The selected compositions of these sets of catalysts were the most actives for ceria-zirconia (20 molar % zirconium) and ceria-praseodymia (50 molar % praseodymia) according to previous studies, and different synthesis methods were used (calcination of nitrates mixture, coprecipitation and reversed microemuslion; all catalysts were calcined at 500ºC, otherwise indicated.

• Request number: 201400533

• Request data:02/07/2014