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The effect of the introduction of heteroelement (Si, P, Al, Ge, Ga and Zr) by direct synthesis on the thermal stability of mesostructured titania prepared by the soft templating pathway has been investigated. All materials have been surfactant-extracted with EtOH and calcined at different temperatures up to 900°C. Ti 4+ can be partially substituted by most of the investigated heteroelements but they mainly form an oxide amorphous phase surrounding the titania anatase particles. Results obtained by SAXS, X-Ray diffraction, Raman spectroscopy and manometry nitrogen adsorption-desorption show that the crystallization of the amorphous titania into nanosized anatase particles and the transition from anatase to rutile occur at higher temperature with the addition of the heteroelement. Even if the lattice distortion introduced by the partial Ti 4+ substitution can participate to this phenomenon, it is mainly due the «glass» effect induced by the presence of the heteroelement in the TiO2 amorphous phase, which limits the growth of the nanosized anatase crystallites. However, when the crystallites reach a limit size, the collapse of the mesostructure occurs. With increasing the calcination temperature, the anatase titania particles become bigger and bigger, the transition from anatase to rutile takes place and the heteroelement can crystallize or be integrated in a crystalline phase. Among the considered heteroelements and by comparison with the bare mesostructured TiO2, the most beneficial effect is obtained in the presence of Si 4+ and PO4 3for which the mesostructure collapse at higher temperature by about two hundred Celsius degrees. Al 3+ and Ge 4+ enhance the thermal stability by about a hundred Celsius degrees and Ga 3+ or Zr 4+ have no significant effect on the temperature at which the mesostructure collapses.

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Here, mixed nanostructured ceria/zirconia oxides have been prepared either by wet impregnation on a nanostructured ZrO2 or by co-condensation through an EISA-derived pathway. This latter method and the impregnation on amorphous ZrO2 followed or not by a 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 XRD and Raman spectroscopy. The surface Ce/Zr molar ratio determined by XPS is very closed to the bulk one, calculated from the X-ray fluorescence analysis. On the opposite, the appearance of nano sized ceria particles with the increase of the cerium content, a monoclinic/tetragonal mixture and an enrichment of the surface in cerium are noted if the impregnation is carried out on a 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 the one of a 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% of CeO2 is almost as efficient as pure ceria.