Probing reoxidation sites by <i>in situ</i> Raman spectroscopy: differences between reduced CeO₂ and Pt/CeO₂

Abstract

Raman spectroscopy is a powerful technique for detecting peroxo (O 2 ) 2– and superoxo (O 2 ) – species adsorbed on defect sites of ceria. These sites are probed by reducing CeO 2 at high temperature and then chemisorbing oxygen species at low temperature. In the present study, it is shown for the first time that such Raman characterization has to be achieved at very low laser power to avoid formation of oxygen species by photolysis and analyze only the chemisorbed species. Respecting this requirement, the (O 2 ) 2– and (O 2 ) – species formed on 0.7% Pt/CeO 2 compound, and the CeO 2 support used to prepare it were compared after reduction for various times and at various temperatures. Superoxo species were more stabilized on reduced 0.7% Pt/CeO 2 after short reduction at 773 K than on reduced CeO 2 . Additionally, the distributions of peroxo species adsorbed on defect sites of Pt/CeO 2 and CeO 2 were significantly different after long reduction at 773 K in spite of similar amounts. Indeed, less stable species were formed during the reduction of 0.7% Pt/CeO 2. These two features revealed that new sites were created during the preparation and reduction of Pt/CeO 2 compared to its bare support. Copyright © 2012 John Wiley &amp; Sons, Ltd.