A Comparison of the Redox Properties of Vanadia-Based Mixed Oxides
By Shah, Parag R.; Khader, Mahmoud M.; Vohs, John M. & Gorte, Raymond J.
Published in The Journal of Physical Chemistry C
2008
Abstract
The thermodynamics of oxidation and reduction were investigated for a series of vanadium-containing oxides, including CeVO4, LaVO4, ZrV2O7, Mg3(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, Mg3(VO4)2, and V2O5.