Dispersion and reactivity of supported vanadium oxide catalysts

Abstract

A series of V2O5/Nb2O5 and V2O5/TiO2 (anatase) catalysts with vanadia loading varying from 2-12 wt% were prepared and characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), electron spin resonance (ESR), BET surface area and oxygen chemisorption at 640 K. The catalytic properties have been evaluated for vapor phase ammoxidation of 3-picoline to nicotinonitrile. XRD results of V2O5/Nb2O5 catalysts suggest the formation of β-(Nb,V)2O5 phase at higher loadings. TPR profiles showed two peaks: the low temperature peak is due to reduction of surface vanadia species and the high temperature peak is due to reduction of Nb2O5. The oxygen uptake increases with increase of vanadia loading on niobia and titania, whereas the dispersion of vanadia decreases. The ammoxidation activity increases with vanadia loading up to 6 wt%, which corresponds to monolayer coverage and remains constant at higher vanadia loadings. The catalytic properties during ammoxidation of 3-picoline are related to the oxygen chemisorption sites.