A new approach of CeO2 and La2O3 effects on the three-way catalysts containing low precious metals

A series of three-way catalysts (TWCs), containing a snail amount of precio us metals (PMs;, including Pt, Pd and Ph) and a large amount of promoters C eO2 and La2O3, were prepared with different precursor compounds and various doped manners. Crystal phases, dispersion of cerium and lanthanum, textura l structure and thermal stability of the catalysts were investigated by XRD , XPS and pore parameters determination. The catalytic performance was stud ied by the measurements of CO, C3H6 and NO conversions on dependence of tem perature at stoichimetric number point (S = 1.00), and from S = 0.75 to 1.3 0 at 280 degrees C or 340 degrees C for fresh or aged samples, respectively . The correlation between the catalytic performance and the characteristics of fresh and aged samples were discussed. The results show that the sample , in which CeO2 and La2O3 are doped with mixed oxide powders, possesses poo r dispersion and less thermal stability, and the conversions of NO and C3H6 are apparently lower than those of the samples aged at 850 degrees C. The main reason is due to the lanthanum enrichment on the surface. The precious metals and cerium may be covered and enveloped, and the PMs located on the internal microporous surface where no cerium and lanthanum exist, are easi er to sinter and oxidize. For the sample doped with La(NO3)(3) and Ce(NO3)( 3) aqueous solutions, high dispersion and thermal stable CeO2-La2O3 solid s olution on all the surface of microporous gamma-Al2O3 Is identified. The so lid solution CeO2-La2O3, also possessed high dispersion in the sample doped with La2O3 powder and Ce(NO3)(3) aqueous solution. The last two aged sampl es keep higher NO conversion at S greater than or equal to 1 region.