Reactivity of some vanadium oxides: An EPR and XRD study

V2O5, VO2 and V2O3 fresh samples and at different times after purchase or preparation (aged samples) were investigated by chemical analysis, redox treatments, XRD and EPR. The ageing process through a reaction with water and oxygen slowly oxidize crystalline VO2 and V2O3, leading to a quasi-amorphous phase with bariandite structure (V10O24·12H2O). The role of water is the progressive demolition of the compact structures and formation of hydrated phase. Kinetic study of VO2 oxidation by O2 and O2+H2O mixture indicates that increasing the temperature up to 723 K the effect of water becomes less important. The reaction leads to partially oxidized products with decreasing water content: bariandite at room temperature, V3O7·H2O at 383 K and V3O7 at 723 K. Kinetic investigation of V2O5 reduction by CO at 633–723 K showed that the reduction process proceeds trough the formation of V4+ and of electrons delocalized in the conduction band.