Kinetics of Palladium Oxidation in the mbar Pressure Range: Ambient Pressure XPS Study

Dmitry Zemlyanov, Birck Nanotechnology Center, Purdue University; University of Limerick
Bernhard Klötzer, University of Innsbruck
Harald Gabasch, University of Innsbruck
Andrew Smeltz, Purdue University
Fabio H. Ribeiro, Purdue University
Spiros Zafeiratos, Max Planck Society
Detre Teschner, Max Planck Society
Peter Schnoerch, Max Planck Society
Elaine Vass, Max Planck Society
Michael Haevecker, Max Planck Society
Axel Knop-Gericke, Max Planck Society
Robert Schloegl, Max Planck Society

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Palladium oxidation was studied by ambient-pressure X-ray photoelectron spectroscopy in the mbar pressure range on the Pd(111) and Pd(110) surfaces. The oxidation kinetics on both surfaces show an induction period when the oxidation rate was low at the beginning and then accelerated. The slow initial oxidation is governed by (a) the rate of nucleus formation, and (b) the rate of oxide nucleus growth. Depth profiling varying photon energy/kinetic photoelectron energy pointed to a 3D oxidation. It is remarkable that the oxidation of Pd(110) proceeds at similar to 100 K lower temperatures than on Pd(111). We suggest that at the high temperature required on Pd(111) nucleation is thermodynamically controlled, and therefore, the nucleation rate decreases with temperature. On Pd(110), nucleation is predominantly kinetically controlled and thus the oxidation rate increases with temperature.


Nanoscience and Nanotechnology