Surface and structural properties of zirconia-supported vanadium oxide. Influence of the preparation pH

Zirconia-supported vanadium oxide catalysts were prepared by equilibrium adsorption in acid (pH 2.7) or basic (pH 10) conditions using hydrous zirconium oxide and an aqueous solution of ammonium metavanadate. The samples, containing vanadium up to 22.24 wt.%, heated at 823 K for 5 h in air, were studied as prepared and after leaching with an ammonia solution by X-ray diffraction, X-ray photoelectron spectroscopy, diffuse optical reflectance, surface area measurements and pore size distribution determination. Owing to the microporous support and to the different condensation degree of the vanadium species, the precursors showed distinct features. The diversity persisted after heating and became more evident at increasing vanadium content. At similar vanadium loading, the fraction in a dispersed state and thus interacting with the support was higher in samples at pH 10 than in those prepared at pH 2.7. For pH 2.7 samples, heating favoured the formation of V2O5 and of ZrV2O7. The interaction between the vanadium dispersed species and the zirconia surface strongly affected the texture, sintering and phase transition of the support.