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Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P303
Growth and Oxidation of Pd/α-Al2O3(0001) Nanoparticles studied with
Synchrotron X-ray Diffraction
Philipp Nolte 1 , N. Kasper 1 , A. Stierle 1 , H. Dosch 1
1 Max Planck Instute for Metals Research, Heisenbergstr. 3, 70569 Stuttgart
Supported transition metal nanoparticles are used as model catalysts. The oxidation
of such systems is of great interest as not only the pure metal, but also its oxides
can be involved in a catalytic process. In addition to bulk single crystal surfaces, the
oxidation properties of nanoparticles can be expected to depend on the support, the
orientation and the particle size. In-situ x-ray diffraction is an appropriate method to
follow structural changes of oxygen induced phase transformations and simultaneously
allows to bridge the pressure gap of UHV based surface analysis techniques.
Pd nanoparticles were grown on α-Al2O3(0001) by electron beam evaporation in UHV
and were studied with SXRD at the MPI-MF beamline at the synchrotron ANKA (FZ
Karlsruhe). It was observed that the particles mainly grow (111)-oriented and epitaxially
with a typical height of 2 nm and a lateral diameter of 4 nm in coexistence with
particles in (110)-orientation. Oxidation experiments were performed in a temperature
range between room temperature and 350 ◦ C.
Applying UHV near oxygen pressures, it could be observed a reversible decrease of
intensity and a broadening of the Pd Bragg peaks. At 350 ◦ C, the formation of bulk
oxide could be observed at an oxygen pressure of 5 mbar. This indicates a structural
change at the Pd particle surface at low oxygen pressures which acts as a kinetic barrier
for the formation of the thermodynamically stable bulk oxide.
Financial support of this work is acknowledged from the European Union under contract
no. NMP3-CT-2003-505670 (NANO2).