Nanoporous CeO₂–ZrO₂ Oxides for Oxidation of Volatile Organic Compounds

Here, mixed nanostructured ceria/zirconia oxides have been prepared either by wet impregnation on nanostructured ZrO2 or by co-condensation through an evaporation-induced self-assembly (EISA)-derived pathway. This latter method and impregnation on amorphous ZrO2, followed or not by heating at 480 °C, lead to a uniform cerium distribution in the zirconia framework, and solid solutions are formed. Stabilization of the tetragonal structure of nano-ZrO2 with the increase of the cerium content is observed by X-ray diffraction (XRD) and Raman spectroscopy. The surface Ce/Zr molar ratio determined by X-ray photoelectron spectrometry (XPS) is very close to the bulk one, calculated from the X-ray fluorescence analysis. In contrast to the appearance of nanosized ceria particles with the increase of the cerium content, a monoclinic/tetragonal mixture and enrichment of the surface in cerium are noted if the impregnation is carried out on nanostructured ZrO2 previously calcined at 480 °C. The obtained catalysts have been tested for the oxidation of toluene, used as a model volatile organic compound. The catalytic efficiency of the mixed oxides has also been compared to that of pure commercial ceria. Results show that the preparation method has a significant effect on the catalytic properties of the materials. Although pure ceria presents the best activity and selectivity, the nanostructured ZrO2 previously calcined at 480 °C and impregnated by 10 mol % CeO2 is almost as efficient as pure ceria.