Characterization of vanadium oxide on ZrO2-based catalyst precursors

Zirconia-supported vanadium oxide catalysts precursors were prepared by equilibrium adsorption in acid (pH 2.7) and basic (pH 10) conditions using hydrous zirconium oxide, ZrO2(383). After drying at 383 K the solids, containing vanadium up to 8.94%, were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse optical reflectance, surface area, differential thermal analysis measurements and chemical determinations. Samples of definite grain size ranges of ZrO2(383) were also investigated. The results show that the pH affects the uptake and the nature of the V adsorbed species. The microporous nature of the support and the different anions size (small vanadium species at pH 10; large polyoxoanions at pH 2.7) affect the spreading degree of vanadium species. Under ambient conditions, the molecular state of the adsorbed species depends on the net surface pH at the point zero charge, that in its turn, is affected by the vanadium loading. During heating, the dispersed species interact with the zirconia surface. The DTA results indicate that the fraction of zirconia involved in the interaction depends on the pH of preparation.