Dresden 2009 – wissenschaftliches Programm

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SYCR: Symposium Chemical Reactions on Nanomaterials: Progress from in-situ Experimental Studies and Theoretical Investigations

SYCR 1: Chemical Reactions on Nanomaterials

SYCR 1.3: Hauptvortrag

Donnerstag, 26. März 2009, 15:00–15:30, BAR SCHÖ

Low dimensional surface oxides in the oxidation of Rh particles — •Florian Mittendorfer — Faculty of Physics, Univ. Vienna, Austria

Transition metal particles are commonly used catalysts for a wide range of oxidation reactions. Accordingly, a wealth of surface science studies has been dedicated to the investigation of the adsorption of oxygen on the low-indexed metal surfaces. Nevertheless, most of the studies have been performed in ultrahigh vacuum, and only in the recent years the research performed under higher pressures has led to the discovery of ultra-thin surface oxide films present under realistic conditions.

We have studied the surface oxides formed on various facets of Rh with the help of density functional (DFT) calculations using the Vienna Ab-initio Simulations Package (VASP). We find the formation of 2-dimensional surface oxides with a common structure on all three low-indexed surfaces, while the presence of step edges leads to the formation of 1-dimensional oxide stripes on the higher indexed surfaces.

The surface oxides play an important role for two different aspects of the oxidation process: On the one hand the thermodynamic stability of the 2D oxides results in an increased presence of low-indexed facets of Rh nanoparticles at high oxygen partial pressures. On the other hand the 1D oxides are a nucleation center for the formation of 2D oxides. The different structures of the 1D oxides present at the step edges lead to a preferred growth direction of the 2D oxides, in agreement with experimental data.