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J. Gustafson, R. Westerström, A. Resta, A. Mikkelsen, J.N. Andersen, O. Balmes, X. Torrelles, M. Schmid, P. Varga, B. Hammer, G. Kresse, C. Baddeley, E. Lundgren:
"Structure and catalytic reactivity of Rh oxides";
Catalysis Today, 145 (2009), 227 - 235.

Using a combination of experimental and theoretical techniques, we show that a thin RhO2 surface oxide
film forms prior to the bulk Rh2O3 corundum oxide on all close-packed single crystal Rh surfaces. Based
on previous reports, we argue that the RhO2 surface oxide also forms on vicinal Rh surfaces as well as on
Rh nanoparticles. The detailed structure of this film was previously determined using UHV based
techniques and density functional theory. In the present paper,we also examine the structure of the bulk
Rh2O3 corundum oxide using surface X-ray diffraction. Being armed with this structural information, we
have explored the CO oxidation reaction over Rh(1 1 1), Rh(1 0 0) and Pt25Rh75(1 0 0) at realistic
pressures using in situ surface X-ray diffraction and online mass spectrometry. In all three cases we find
that an increase of the CO2 production coincides with the formation of the thin RhO2 surface oxide film.
In the case of Pt25Rh75(1 0 0), our measurements demonstrate that the formation of bulk Rh2O3
corundum oxide poisons the reaction, and argue that this is also valid for all other Rh surfaces. Our study
implies that the CO oxidation reaction over Rh surfaces at realistic conditions is insensitive to the exact
Rh substrate orientation, but is rather governed by the formation of a specific surface oxide phase.