Zusammenfassung
The interaction of oxygen with Pd particles, vapor deposited onto
a thin alumina film grown on a NiAl(1 1 0) substrate, was studied
by STM, AES, LEED, XPS, TPD and molecular beam techniques. The results
show that O2 exposure at 400�500 K strongly influences the oxide
support. We suggest that the oxygen atoms formed by dissociation
on the Pd surface can diffuse through the alumina film and react
with the NiAl substrate underneath the Pd particles, thus increasing
the thickness of the oxide film. The surface oxygen inhibits hydrogen
adsorption, and readily reacts with CO at 300�500 K. For large and
crystalline Pd particles, the system exhibits adsorption�desorption
properties which are very similar to those of the Pd(1 1 1) single
crystal surface. The molecular beam and TPD experiments reveal that,
at low coverage, CO adsorbs slightly stronger on the smaller Pd particles,
with an adsorption energy difference of \sim5�7 kJ mol-1 for 1 and
3�5 nm Pd particles studied.
Nutzer