Doped nanosized ceria solid solutions for low temperature soot oxidation: Zirconium versus lanthanum promoters

The relative efficacies of zirconium and lanthanum promoters in ceria solid solutions were investigated systematically for low temperature soot oxidation. Thus nanosized CeO2-ZrO2 (CZ, 1:1) and CeO2-La2O3 (CL, 8:2) solid solutions, and a reference CeO2 (C) were synthesized and investigated by means of various characterization techniques namely, XRD. TEM, BET surface area, XPS, UV-vis DRS. Raman and TPR. The catalytic efficiency for oxygen storage/release capacity (OSC) and soot oxidation were evaluated by a thermogravimetric (TG) method. The XRD results suggested formation of solid solutions and TEM studies confirmed nanosized nature of the particles. Raman and XPS measurements disclosed the presence of oxygen vacancies and lattice defects in both CZ and CL samples and these were more prominent in the case of CL sample. XPS studies revealed existence of both Ce3+ and Ce4+ (confirming redox nature), and the concentration of former is relatively higher in CL sample. The CL solid solution exhibited high intense and more resolved O2- -> Ce3+ charge transfer transition band compared to CZ in the UV-vis DRS study. TPR measurements indicated a facile reduction of ceria after La3+ incorporation. Activity studies revealed that La3+ doped ceria accelerates the oxidation rate of soot compared to pure ceria and Zr4+ doped ceria. An attempt has been made to explain the enhanced activity of CL sample in terms of active oxygen formation provoked by defective structure of ceria due to the presence of La3+. (C) 2010 Elsevier B.V. All rights reserved.