Characterization and reactivity of vanadium oxide catalysts supported on niobia

A series of V2O5/Nb2O5 catalysts with vanadia loading varying from 2 to 12 wt.% were prepd. and characterized by X-ray diffraction (XRD), XPS, temp. programmed redn. (TPR), BET surface area and oxygen chemisorption at 640 K. The catalytic properties have been evaluated for vapor phase ammoxidn. of 3-picoline to nicotinonitrile. XRD results suggest the formation of b-(Nb,V)2O5 phase at higher loadings. TPR profiles showed two peaks: the low temp. peak is due to redn. of surface vanadia species and the high temp. peak is due to redn. of Nb2O5. XPS results reveal that both vanadia and niobia are present in fully oxidized state (5+) in all the samples. The intensity ratio V 2p3/2:Nb 3d5/2 is found to increase with increase in vanadia loading up to 6 wt.% and to remain const. at higher vanadia loadings. The oxygen uptake increases with increase of vanadia loading on niobia, whereas the dispersion of vanadia decreases. The dispersion of vanadia measured by oxygen chemisorption method is in good agreement with the dispersion detd. from XPS. The ammoxidn. activity increases with vanadia loading up to 6 wt.%, which corresponds to monolayer coverage and remains const. at higher vanadia loadings. The catalytic properties during ammoxidn. of 3-picoline are related to the oxygen chemisorption sites. [on SciFinder (R)