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 CeVO 4, LaVO 4, ZrV 2 O 7, Mg 3 (VO 4 ) 2, CrVO 4, AlVO 4, and V 2 O 5, 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 V 2 O 5 and ZrV 2 O 7, 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. CrVO 4 and AlVO 4 were unstable to deep reduction, but oxidation enthalpies and entropies were reported for CeVO 4, ZrV 2 O 7, Mg 3 (VO 4 ) 2, and V 2 O 5 .