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Evolution of VPO and VOx catalysts under conventional XPS conditions: the role of support effects
|Yuri Suchorski 1, Michael Schulz 1, Frank Klose 2, Liisa Rhiko-Struckmann 2, Yinmei Ye 2, Maia Alandjiyska 1, Helmut Weiss 1|
1. Otto-von-Guericke-Universitaet Magdeburg, Chemisches Institut, Universitaetsplatz 2, Magdeburg D-39106, Germany
The stability of VPO and different supported VOx catalysts for partial oxidation of small hydrocarbons under the ultra-high vacuum (UHV) conditions of standard X-ray photoelectron spectroscopy (XPS) was studied using a multi-purpose surface analysis apparatus which allows time spans of only a few minutes between the sample transfer into vacuum and the first photoelectron spectrum. The VPO catalysts showed a significant dependence of the vanadium oxidation state upon the time of exposure to UHV, as determined from the shape evolution of the V2p3/2 peak. The initial VV/VIV ratio was found to decrease by a factor of at least ~2 within the first 15 - 25 min of the XPS experiment for fresh as well as used VPO catalysts. From a careful set of experiments in a "stop and go" mode (10 to 20 s) of the X-ray source it can be concluded that the observed changes are predominantly due to the vacuum environment, with a rather minor (if at all) contribution of the X-ray excitation.
Presentation: poster at E-MRS Fall Meeting 2004, Symposium I, by Yuri Suchorski
See On-line Journal of E-MRS Fall Meeting 2004
Submitted: 2004-06-04 13:36 Revised: 2009-06-08 12:55