Studies on dispersion and reactivity of vanadium oxide catalysts supported on titania

Vanadium oxide catalysts with V2O5 loadings ranging from 2 to 12% w/w supported on various modifications of titania have been prepared by the wet impregnation method. The calcined samples were characterized by X-ray diffraction (XRD), electron spin resonance (ESR), oxygen chemisorption, temperature-programmed desorption (TPD) of ammonia, and surface area measurements. The catalytic properties were evaluated for ammoxidation of 3-picoline to nicotinonitrile. Dispersion of vanadia was determined by the oxygen chemisorption at 640 K and by the static method on the samples prereduced at the same temperature. Oxygen chemisorption results suggest that vanadium oxide disperses better on TiO2 (anatase) than it is supported on TiO2 (rutile) or TiO2 containing mixture of anatase and rutile. ESR spectra obtained under ambient conditions for the catalysts reduced at 640 K show the presence of V4+ ions in axial symmetry. The results of XRD and ESR substantiate the findings of oxygen chemisorption. Ammonia TPD results suggest that V2O5 supported on anatase is more acidic than V2O5 supported on TiO2 (rutile) or TiO2 (rutile and anatase). V2O5-supported anatase TiO2 exhibited higher activities for 3-picoline ammoxidation than V2O5/TiO2 (rutile) and V2O5/TiO2 (anatase + rutile). The catalytic properties during ammoxidation are related to the oxygen chemisorption sites.