| Summary: | Three nanostructured catalysts with low total rare earth elements (REEs) content (i.e., 15 mol.%) were prepared by depositing CeO<sub>2</sub> or Ln<sup>3+</sup>-doped CeO<sub>2</sub> (Ln<sup>3+</sup> = Y<sup>3+</sup> or La<sup>3+</sup>; Ln/Ce = 0.15) on the surface of ZrO<sub>2</sub> nanoparticles, as nanometre-thick, fluorite-type clusters. These samples were subjected to successive reduction treatments at increasing temperatures, from 500 to 900 °C. A characterisation study by XPS was performed to clarify the diffusion process of cerium into the bulk of ZrO<sub>2</sub> crystallites upon reduction to yield Ce<sub>x</sub>Zr<sub>1</sub><sub>−</sub><sub>x</sub>O<sub>2</sub><sub>−</sub><sub>δ</sub> surface phases, and the influence of the incorporation of non-reducible trivalent REE cations, with sizes smaller (Y<sup>3+</sup>) and larger (La<sup>3+</sup>) than Ce<sup>4+</sup> and Ce<sup>3+</sup>. For all nanocatalysts, a reduction treatment at a minimum temperature of 900 °C was required to accomplish a significant cerium diffusion. Notwithstanding, the size of the dopant noticeably affected the extent of this diffusion process. As compared to the undoped ZrO<sub>2</sub>-CeO<sub>2</sub> sample, Y<sup>3+</sup> incorporation slightly hindered the cerium diffusion, while the opposite effect was found for the La<sup>3+</sup>-doped nanocatalyst. Furthermore, such differences in cerium diffusion led to changes in the surface and nanostructural features of the oxides, which were tentatively correlated with the redox response of the thermally aged samples.
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