Evolution of VPO and VOx catalysts under conventional XPS conditions: the role of support effects

Yuri Suchorski 1Michael Schulz 1Frank Klose 2Liisa Rhiko-Struckmann 2Yinmei Ye 2Maia Alandjiyska 1Helmut Weiss 1

1. Otto-von-Guericke-Universitaet Magdeburg, Chemisches Institut, Universitaetsplatz 2, Magdeburg D-39106, Germany
2. Max-Planck-Institut für Dynamik komplexer technischer Systeme, Magdeburg, Germany

Abstract

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.
In contrast to these results on VPO, the investigated VOx catalysts on various support materials, like Al2O3, TiO2 and SiO2, change under the same conditions to a much lesser degree and on the time scale of hours instead of minutes. The role of the V-O-support bonds has been studied by variation of the support at nearly constant vanadium concentration, and the stabilizing effect of the supporting oxide material on the vanadium oxidation state is discussed.

Legal notice
  • Legal notice:

    Copyright (c) Pielaszek Research, all rights reserved.
    The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
    In every case, proper references including Author(s) name(s) and URL of this webpage: http://science24.com/paper/2288 must be provided.

 

Related papers
  1. Surface chemistry of Pr-doped nanocrystalline zirconia
  2. Field-induced electron density redistribution at carbon surface: many body effects
  3. Catalytic reactions on platinum metals nanofacets: Spectroscopy on an atomic scale
  4. Determination and fine tuning of the cerium oxidation state in cerium calixarene complexes
  5. CATALYTIC REACTIONS ON NANOSIZED SURFACES: BRIDGING OF THE MATERIALS AND PRESSURE GAP

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
Google
 
Web science24.com
© 1998-2021 pielaszek research, all rights reserved Powered by the Conference Engine