Bulk and surface structures of iron doped zirconium oxide systems: Influence of preparation method

Three different Fe-Zr oxide systems were prepared using firstly classical impregnation of iron nitrates on calcined ZrO2 (Fex/ZrO2, x represents Fe/Zr ratio = 0.01 and 0.11), secondly impregnation of iron nitrates on dried zirconium hydroxide ZrO(OH)2 (Fex/ZrO(OH)2) and finally hydrolysis of aqueous suspension of iron and zirconium salts to coprecipitate iron and zirconium hydroxides (Fex-Zr). Thermal decomposition study of dried samples evidenced a delay in the temperature crystallization of zirconia for Fex-Zr and Fex/ZrO(OH)2, the more the iron content in the sample, the more important the delay. For these samples, the formation and the stabilization of different phases were evidenced by several characterization techniques : X-Ray Diffraction (XRD), Raman spectroscopy and Electron Paramagnetic Resonance (EPR). The interaction of iron species with zirconia was different in accordance with different preparations. A bulk dispersion of the coprecipitated sample was observed and as a consequence Zr3+ defects in the solid were not produced. In the case of Fex/ZrO2 sample, production of surface Zr3+ ions was established at low temperature of calcination (up to 600◦C) and explained by the reaction of NO−3 with Zr4+ on the zirconia surface. However such interaction did not occur for Fex/ZrO(OH)2 since a low dispersion of iron species was observed by X-ray Photoelectron Spectroscopy (XPS), deposited phase (Fe2O3) forming preferentially blocks. Temperature Programmed Reduction (TPR) showed that the reduction of small particles of Fe2O3 and bulk Fe2O3 present in the impregnated samples was easier than that of iron species well dispersed in the bulk of the coprecipitated solid. C 2005 Springer Science + Business Media, Inc.