A comparison of the redox properties of vanadia-based mixed oxides

The thermodynamics of oxidation and reduction were investigated for a series of vanadium-containing oxides, including CeVO4, LaVO4, ZrV2O7, Mg-3(VO4)(2), CrVO4, AlVO4, and V2O5, in the temperature range between 873 and 973 K, using coulometric titration to measure oxidation isotherms. For each of the compounds, the oxygen uptakes corresponded to oxidation from V+3 to V+5 as oxygen fugacities increased from 10(-25) to 10(-2) atm. With V2O5 and ZrV2O7, the only materials in this group that contain V-O-V linkages, there was evidence for two oxidation processes, corresponding to V+3-V+4 and V+4-V+5 equilibria, whereas oxidation occurred in a single step for the other materials. CrVO4 and AlVO4 were unstable to deep reduction, but oxidation enthalpies and entropies were reported for CeVO4, ZrV2O7, Mg-3(VO4)(2), and V2O5.