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O: Oberflächenphysik

O 4: Epitaxie und Wachstum I

O 4.6: Vortrag

Freitag, 4. März 2005, 12:00–12:15, TU EB202

Electronic structure of Zn on Pd(111) during growth and alloying — •Andreas Bayer, Ken Flechtner, Dieter Borgmann, Reinhard Denecke, and Hans-Peter Steinrück — Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91058 Erlangen

Hydrogen as energy carrier can be produced by steam reforming of methanol over Pd/ZnO catalysts. The high activity and selectivity of the catalysts is attributed to the in-situ formation of Pd-Zn alloys as one of the active components [1]. Therefore, we investigated the growth of thin Zn layers (0-3 ML) on Pd(111) at 105 K and the changes in electronic structure during subsequent annealing to higher temperatures (up to 1000 K) by high-resolution X-ray photoelectron spectroscopy (XPS) with monochromized Al K_α radiation, ultraviolet photoelectron spectroscopy (UPS), and low energy electron diffraction (LEED). The formation of Pd-Zn alloys above 300 K can clearly be seen in XP spectra, as new Zn 2p_3/2 and Pd 3d_5/2 peaks evolve. The temperatures, at which these alloys form, strongly depend on the amount of adsorbed Zn. An ordered alloy was only observed for annealing 1 ML of Zn to 400-600 K. UPS measurements show a reduction in the density of states near the Fermi edge during alloying, explaining the Cu-like catalytic behaviour.

Supported by the DFG (Schwerpunktsprogramm 1091, Ste620/3-3).

[1] N. Iwasa, S. Masuda, N. Ogawa, and N. Takezawa, Appl. Catal. A 125 (1995) 145