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Catalysis Letters

, 125:1 | Cite as

Redox Isotherms for Vanadia Supported on Zirconia

  • Parag R. Shah
  • John M. Vohs
  • Raymond J. Gorte
Article

Abstract

Redox isotherms were measured for zirconia-supported vanadia between 10−2 and 10−28 atm at 748 K for two vanadia loadings, 2.9 and 5.8 V/nm2, corresponding to isolated VO4 species and monolayer, polymeric vanadates. The catalyst with isolated VO4 species, which is expected to have predominantly V–O–Zr linkages, had a redox isotherm that showed a well-defined step corresponding to one oxygen per V. By contrast, the redox isotherm for the catalyst with polymeric vanadates changed more gradually with \( \hbox{P}_{{\rm O}_2} \) and the change in the oxygen stoichiometry corresponded to 0.85 O/V. Comparison of these results to the redox isotherms for bulk vanadates suggests that oxidation of the isolated vanadates proceeds by a direct transition from V+3 ↔ V+5, while transitions from V+3 ↔ V+4 and V+4 ↔ V+5 are possible with the polyvanadates. Rate measurements for methanol and propane oxidation over the two supported vanadia catalysts and several bulk vanadates showed that specific rates for each reaction were similar on all of the samples, suggesting that that the V–O bond strength does not affect the rate determining step of these reactions.

Keywords

Supported catalyst Vanadia Vanadium oxide Cerium vanadate Magnesium vanadate Zirconium vanadate Zirconia Coulometric Titration Methanol oxidation Formaldehyde Oxidation Redox Equilibrium Partial oxidation 

Notes

Acknowledgements

The authors would like to acknowledge the Materials Characterization Facility at Drexel University for providing the Raman Spectrometer. This work was supported by the Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division, Grant DE-FG02-85ER13350.

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Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  • Parag R. Shah
    • 1
  • John M. Vohs
    • 1
  • Raymond J. Gorte
    • 1
  1. 1.Department of Chemical & Biomolecular EngineeringUniversity of PennsylvaniaPhiladelphiaUSA

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