Reactivity of some vanadium oxides: An EPR and XRD study

V 2O 5, VO 2 and V 2O 3 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 VO 2 and V 2O 3, leading to a quasi-amorphous phase with bariandite structure (V 10O 24·12H 2O). The role of water is the progressive demolition of the compact structures and formation of hydrated phase. Kinetic study of VO 2 oxidation by O 2 and O 2+H 2O 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, V 3O 7·H 2O at 383 K and V 3O 7 at 723 K. Kinetic investigation of V 2O 5 reduction by CO at 633–723 K showed that the reduction process proceeds trough the formation of V 4+ and of electrons delocalized in the conduction band. XRD diffraction patterns of VO 2 (Aldrich): (a) fresh sample, (b) after 26 months, (c) after 95 months, (d) after 95 months and thermal treatment at 383 K in air, and (c) after 95 months and thermal treatment at 383 K in sealed glass tube.