Probing the Effect of Local Structure on the Thermodynamic Redox Properties of V+5: A Comparison of V2O5 and Mg3(VO4)2

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• 作者：Parag R. Shah ; John M. Vohs ; Raymond J. Gorte
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：May 24, 2007
• 年：2007
• 卷：111
• 期：20
• 页码：5680 - 5683
• 全文大小：81K
• 年卷期：v.111,no.20(May 24, 2007)
• ISSN：1520-5207

文摘

Coulometric titration, an electrochemical method for measuring oxidation isotherms, has been used tocharacterize the redox properties of V₂O₅ and Mg₃(VO₄)₂ between 823 and 973 K. V₂O₅ shows distinct regionsin the isotherms corresponding to equilibrium with mixtures of V₂O₃ and V₂O₄ and of V₂O₄ and V₂O₅. Fromthis data, the enthalpies for oxidation of V₂O₃ to V₂O₄ and for V₂O₄ to V₂O₅ are shown to be -380 ± 10 and-285 ± 20 kJ mol^-1 O₂, respectively. Oxidation isotherms for Mg₃(VO₄)₂ exhibit a single step between theoxidized sample (all V⁺⁵) and a completely reduced sample (all V⁺³). The enthalpy of oxidation is found toincrease with the oxidation state of the sample, from -370 ± 30 kJ mol^-1 O₂ at an O:V ratio of 1.5 to-460 ± 10 kJ mol^-1 O₂ at an O:V ratio of 2.5.