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Simultaneous <i>in situ</i> monitoring of surface and gas species and surface properties by modulation excitation polarization-modulation infrared reflection-absorption spectroscopy: CO oxidation over Pt film
Auteur(s)
Urakawa, Atsushi
Bürgi, Thomas
Schläpfer, Hans-Peter
Alfons Baiker
Date de parution
2006
In
European Journal of Inorganic Chemistry, 2006/124/054717 (11 pages)
Résumé
A method for <i>in situ</i> monitoring of surface and gas species utilizing separately the difference and sum reflectivity of two polarizations, normal and parallel to the surface, measured by polarization-modulation infrared reflection-absorption spectroscopy is presented. Surface and gas-phase spectra were separately but simultaneously obtained from the reflectivities. The technique is combined with modulation excitation spectroscopy to further enhance the sensitivity, and a small-volume cell was designed for this purpose. CO oxidation over a 40 nm Pt film on aluminum was investigated under moderate pressure (atmospheric pressure, 5% CO, and 5%–40% O<sub>2</sub>) at 373–433 K. The surface species involved in the oxidation process and the gas-phase species, both reactant (CO) and product (CO<sub>2</sub>), could be simultaneously monitored and analyzed quantitatively. In addition, the reflectivity change of the sample during the reaction was assigned to a near-surface bulk property change, that is, surface reconstruction to the oxide phase. Under an O<sub>2</sub>-rich atmosphere, two reactive phases, denoted as low- and high-activity phases, were identified. A large amount of atop CO was observed during the low-activity phase, while the adsorbed CO completely disappeared during the high-activity phase. The presence of an infrared-inactive CO<sub>2</sub> precursor formed by the reaction between surface oxide and gaseous CO during the high-activity phase was inferred. The desorption of the CO<sub>2</sub> precursor is facilitated under a CO-rich atmosphere, most likely, by surface reconstruction to metallic Pt and a competitive adsorption of CO on the surface.
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Type de publication
journal article
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