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Not only V(V) - What really is the nature of supported vanadate catalysts?

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http://pubman.mpdl.mpg.de/cone/persons/resource/persons86519

Wolff,  Tanya
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons86390

Lorenz,  Heike
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons86477

Seidel-Morgenstern,  Andreas
Otto-von-Guericke-Universität Magdeburg, External Organizations;
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

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Citation

Klose, F., Wolff, T., Lorenz, H., Seidel-Morgenstern, A., Suchorski, Y., Piorkowska, M., et al. (2007). Not only V(V) - What really is the nature of supported vanadate catalysts?. Poster presented at EUROPACAT-VIII, Turku / Åbo, Finland.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0014-7112-3
Abstract
In supported vanadate catalysts the V atoms are commonly assumed to be mostly in oxidation state +5 in the oxidized state. However, H/V ratios of less than 2 are often observed in TPR experiments, and significant fractions of V(IV) species are observed using the XPS, UV-VIS or ESR techniques. The aim of this contribution is to clarify this discrepancy. From the TPR, XPS, BET, XRD, TEM, DRIFTS and pyridine TPD data as well as from a structure-activity analysis in ethane oxidation, it can be concluded that in isolated and polymerized vanadates only 1/3 of V (but 80 % of V in crystalline V2O5 phases) can reach the oxidation state +5. The other V centers remain at oxidation state +4 even after oxidizing or various redox treatments. This implies the existence of two different kinds of V species within the vanadate structures. However, M-O-V(V) bonds as active sites and V=O bonds should be present to reach consistence with spectroscopic data and to explain the support effects. The smallest unit which meets these requirements is [V3O8]3- (3 support bonds) for the isolated vanadates. For polyvanadates a structure with the sequence (-V(IV)-O-V(V)-O-V(IV)-O-)n is postulated.