CONICET | Buscador de Institutos y Recursos Humanos

ZrO2-CeO2 substitutional solid solutions are extensively used as redox or oxygen storage promoters in three-way catalysts, which are applied in controlling the emissions of NOx, CO and hydrocarbons from automotive exhausts. The properties of zirconia-ceria mixed oxides are strongly related to their crystal structure and local order. In particular, the metastable forms of the tetragonal phase have been widely investigated since they are the most suitable for applications. One of the most notable characteristics of some zirconia-based solid solutions is the existence of three tetragonal forms, all belonging to the P42/nmc space group. The stable tetragonal form is called the t-form. There is also a t-form with a wider solubility, but unstable in comparison with the mixture of the t-form and cubic phase. Finally, the t-form has an axial ratio c/a of unity, but with the oxygen atoms displaced along the c axis from their ideal sites of the cubic phase (8c sites of the Fm3m space group).In this work, a detailed crystallographic study performed by X-ray di®raction (XPD 10B beamline of LNLS) was carried out on nanostructured ZrO2-50 and 65%mol CeO2 solid solutions. Both compositions were synthesized by different chemical routes: citrate complexation and gel-combustion (employing lysine and glycine as fuel). The lattice parameters, a and c and the fractional z-coordinate of the O2¡ anion in the tetragonal asymmetric unit, z(O), were re¯ned by Rietveld method. ZrO2-50%mol CeO2 solid solution exhibits the metastable t-form while the t-form is observed in ZrO2-65%mol CeO2. The crystallite size was determined by Scherrers formula. The influence of the synthesis method on the crystal structure of these solid solutions were evaluated.

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