Development of a Ce-Zr-La modified Pt/γ-Al2O3 TWCs' washcoat: Effect of synthesis procedure on catalytic behaviour and thermal durability

In this work the effect of different synthesis routes on the thermal stability and catalytic performance of Ce-Zr-La modified Pt/gamma-Al2O3 three-way converters (TWCs) washcoat is investigated. The production procedures applied were: (i) simultaneous coprecipitation of gamma-alumina and ceria-based solid solution from metal nitrates, (ii) sequential coprecipitation of these components and (iii) wet impregnation with different gamma-alumina powders (a commercial and a precipitated one). The performance of the as produced catalysts, after loading on cordierite monoliths (TWCs form) was studied under simulated exhaust conditions at the stoichiometric point. Structural, morphological and catalytic properties of the washcoats were examined after calcination at 600 degrees C for 2 h and thermal aging at 900 degrees C for 5 h in air. X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Telter physical adsorption (BET) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were applied for the correlation of the samples' catalytic behaviour with their microstructure and morphological characteristics. Among the preparation routes examined simultaneous coprecipitation leads to the most thermally stable washcoat; it was found to provide higher dispersion of the oxide modifiers in the alumina carrier impeding that way Pt sintering. TWCs prepared by this route also showed the best catalytic performance providing the maximum NO, CO and C3H6 conversions and the lowest light-off temperatures. (C) 2009 Elsevier B.V. All rights reserved.