REDOX TRANSFORMATIONS OF SIMPLE VANADIUM PHOSPHATES - THE SYNTHESIS OF EPSILON-VOPO4

A reproducible high yield hydrothermal synthesis of VPO4 . H2O that mi nimizes the amount of organic species adsorbed on the solid particles has been developed. Oxidation of VPO4 . H2O at less than or equal to 5 50 degrees C in oxygen has been shown to result in the formation of a new VOPO4 phase that has been designated epsilon-VOPO4. This new VOPO4 phase is structurally distinct but related to the structures of beta- VOPO4 and VPO4 . H2O. All three phases contain chains of corner-shared vanadium oxygen atom octahedra that are bridged by phosphate groups. The fully oxidized epsilon-VOPO4 is reduced to VPO4 . H2O at 150 degre es C by a topotactic reaction with hydrogen in the presence of platinu m ('hydrogen spillover').