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 small amount of precious metals (PMs, including Pt, Pd and Rh) and a large amount of promoters CeO2 and La2O3, were prepared with different precursor compounds and various doped manners. Crystal phases, dispersion of cerium and lanthanum, textural structure and thermal stability of the catalysts were investigated by XRD, XPS and pore parameters determination. The catalytic performance was studied by the measurements of CO, C3H6 and NO conversions on dependence of temperature at stoichimetric number point (S = 1.00), and from S = 0.75 to 1.30 at 280°C or 340°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 mat the sample, in which CeO2 and La2O3 are doped with mixed oxide powders, possesses poor dispersion and less thermal stability, and the conversions of NO and C3H6 are apparently lower man those of the samples aged at 850°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 easier 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 solution on all the surface of microporous γ‐Al2O3 is identified. The solid solution CeO2La2O3 also possessed high dispersion in Ok sample doped with La2O3 powder and Ce(NO3)3 aqueous solution. The last two aged samples keep higher NO conversion at S≥1 region.