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

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 CeO2 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/CeO2 compound, and the CeO2 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/CeO2 after short reduction at 773 K than on reduced CeO2. Additionally, the distributions of peroxo species adsorbed on defect sites of Pt/CeO2 and CeO2 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/CeO2. These two features revealed that new sites were created during the preparation and reduction of Pt/CeO2 compared to its bare support. Copyright (C) 2012 John Wiley & Sons, Ltd.