Vanadium oxide catalysts with V2O5 loadings ranging from 2 to 12% w/w suppo
rted on various modifications of titania have been prepared by the wet impr
egnation method. The calcined samples were characterized by X-ray diffracti
on (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 nicot
inonitrile. Dispersion of vanadia was determined by the oxygen chemisorptio
n at 640 K and by the static method on the samples prereduced at the same t
emperature. Oxygen chemisorption results suggest that vanadium oxide disper
ses better on TiO2 (anatase) than it is supported on TiO2 (rutile) or TiO2
containing mixture of anatase and rutile. ESR spectra obtained under ambien
t conditions for the catalysts reduced at 640 K show the presence of V4+ io
ns 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 (rutil
e and anatase). V2O5-supported anatase TiO2 exhibited higher activities for
3-picoline ammoxidation than V2O5/TiO2 (rutile) and V2O5/TiO2 (anatase + r
utile). The catalytic properties during ammoxidation are related to the oxy
gen chemisorption sites.