Preparation of CeZr1-xO2 (x=0.75, 0.62) solid solution and its application in Pd-only three-way catalysts

Nanoparticles of CexZr1-xO2 (x = 0.75, 0.62) were prepared by the oxidation-coprecipitation method using H2O2 as an oxidant, and characterized by N-2 adsorption, XRD and H-2-TPR. CexZr1-xO2 prepared had single fluorite cubic structure, good thermal stability and reduction property. With the increasing of Ce/Zr ratio, the surface area of CexZr1-xO2 increased, but thermal stability of CexZr1-xO2 decreased. The surface area of Ce0.62Zr0.38O2 was 41.2 m(2)/g after calcination in air at 900 degrees C for 6 h. TPR results showed the formation of solid solution promoted the reduction of CeO2, and the reduction properties of CexZr1-xO2 were enhanced by the cycle of TPR-reoxidation. The Pd-only three-way catalysts (TWC) were prepared by the impregnation method, in which Ce0.75Zr0.25O2 was used as the active washcoat and Pd loading was 0.7 g/L. In the test of Air/Fuel, the conversion of C3H8 was close to 100% and NO was completely converted at lambda < 1.025. The high conversion of C3H8 was induced by the steam reform and dissociation adsorption reaction of C3H8. Pd-only catalyst using Ce0.75Zr0.25O2 as active washcoat showed high light off activity, the reaction temperatures (T-50) of 50% conversion of CO, C3H8 and NO were 180, 200 and 205 degrees C, respectively. However, the conversions of C3H8 and NO showed oscillation with continuously increasing the reaction temperature. The presence of La2O3 in washcoat decreased the light off activity and suppressed the oscillation of C3H8 and NO conversion. After being aged at 900 'C for 4 h, the operation windows of catalysts shifted slightly to rich burn. The presence of La2O3 in active washcoat can enhance the thermal stability of catalyst significantly. (C) 2007 Elsevier B.V. All rights reserved.