Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 33: Symposium: Frontiers of Surface Sensitive Electron Microscopy I (Invited Speakers: James Hannon, Raoul van Gastel, Thomas Schmidt)

O 33.4: Vortrag

Dienstag, 26. Februar 2008, 15:00–15:15, MA 005

Structural imaging of surface oxidation and oxidation catalysis on transition metal surfaces — •Jan Ingo Flege and Peter Sutter — Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, United States

The oxides of 4d late transition metals (TM), such as ruthenium and rhodium, are a class of materials with desirable functional properties, e. g., for catalysis. However, the mechanism of initial oxidation of these materials and the nature of the structures produced by facile oxygen uptake into sub-surface layers have been notoriously difficult to investigate experimentally, primarily because of a lack of spatially resolving and structurally sensitive techniques adequate for identifying the initial nanometer-sized oxidation products under reaction conditions.

Here we use spatially and temporally resolved structural fingerprinting in connection with multiple scattering calculations to characterize surface oxidation as well as the catalytic properties of the resulting oxygen-rich structures on Ru(0001) and Rh(111). We will show that for both Ru and Rh the initial oxidation proceeds by initial formation of a O-TM-O trilayer. However, while in the case of Rh the thicker oxide structures emerge from the trilayer surface oxide, the bulk oxide RuO₂(110) islands grow independently from the trilayer, competing for surface area. Furthermore, individual phase-specific chemical reactivities for CO oxidation and cooperative effects during the catalytic cycle induced by the nanoscale heterogeneity will be discussed.