ESR spectroscopic characterization of V2O5/AlF3 ammoxidation catalysts

Abstract

Electron spin resonance (ESR) spectroscopic study has been made at 25 °C on a series of V2O5/AlF3 catalysts, prepared by wet impregnation method with different V2O5 loadings ranging from 2 to 15 wt%. V2O5/AlF3 solids have been used as catalysts in the ammoxidation of 3-picoline to nicotinonitrile. The ESR parameters like gshort parallel, gperpendicular, Ashort parallel, Aperpendicular were obtained from the spectra from which isotropic g factor (g0), isotropic hyperfine interaction factor (A0) and bonding parameters (α2, β22, B, C, K) were calculated. The well-resolved ESR spectra of catalysts indicate the paramagnetic nature of V4+ (VO2+) species on the AlF3 support, which are in the distorted octahedral environment. The integral intensity of V4+ species and the selectivity to nicotinonitrile are increasing with increase in V2O5 loading, which may be due to facile redox mechanism (V4+/V5+) or the progressive increase in V4+ interaction along with V2O5 loading.