Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 8, Issue 1, Pages 102-108Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.6b02314
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Funding
- Swiss National Science Foundation [200021_140750]
- Swiss National Science Foundation (SNF) [200021_140750] Funding Source: Swiss National Science Foundation (SNF)
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X-ray photoelectron spectroscopy has been employed for the qualitative and quantitative characterization of both model and real catalytic surfaces. Recent progress in the detection of photoelectrons has enabled the acquisition of spectra at pressures up to a few tens of millibars. Although reducing the pressure gap represents a remarkable advantage for catalysis, active sites may be short-lived or hidden in the majority of spectator species. Time-resolved experiments, conducted under transient conditions, are a suitable strategy for discriminating between active sites and spectators. In the present work, we characterized the surface of a Pt/CeO2 powder catalyst at 1.0 mbar of a reacting mixture of carbon monoxide and oxygen and, by means of time resolution, identified short-lived active species. We replaced oxygen with nitrogen in the reaction mixture while fast-detecting the core level peaks of cerium. The results indicate that active Ce3+ sites form transiently at the surface when the oxygen is switched off. Analysis of the depth profile shows that CO' ions are located at the ceria surface. The same experiment, performed on platinum-free ceria, reveals negligible reduction, indicating that platinum boosts the formation of CO3+ active sites at the interface.
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