CHARACTERIZATION OF SUPPORTED VANADIUM-OXIDE CATALYSTS BY A LOW-TEMPERATURE OXYGEN-CHEMISORPTION TECHNIQUE .3. THE V2O5/ZRO2 SYSTEM ALPHA

Low-temperature oxygen chemisorption (LTOC) has been applied to characterize a series of V2O5/ZrO2 catalysts containing up to 10.38% of V2O5. The catalysts were also characterized by X-ray diffraction (XRD), and electron spin resonance (ESR). Oxygen chemisorption results suggest the formation of a monolayer of vanadium oxide at a concentration of about 6.53 wt.-% with a high degree of dispersion of vanadia on ZrO2. X-ray diffraction studies revealed that the phase transition of ZrO2 (monoclinic to tetragonal) is catalyzed by the presence of vanadia on the support. The ESR results have also shown that the chemical species on the surface and their structure are more affected by the vanadia loading. Oxygen chemisorption capacities of the catalysts were found to correlate with the activities of the catalysts for the partial oxidation of methanol to formaldehyde. A comparison of LTOC results of vanadia supported on zirconia with those of vanadia supported on alumina, silica and titania suggests that the vanadium oxide disperses better on zirconia.