Interaction of Au with
Thin ZrO<sub>2</sub> Films:
Influence of ZrO<sub>2</sub> Morphology on the Adsorption and Thermal
Stability of Au Nanoparticles
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Abstract
The model catalysts of ZrO<sub>2</sub>-supported Au nanoparticles
have been prepared by deposition of Au atoms onto the surfaces of
thin ZrO<sub>2</sub> films with different morphologies. The adsorption
and thermal stability of Au nanoparticles on thin ZrO<sub>2</sub> films
have been investigated using synchrotron radiation photoemission spectroscopy
(SRPES) and X-ray photoelectron spectroscopy (XPS). The thin ZrO<sub>2</sub> films were prepared by two different methods, giving rise
to different morphologies. The first method utilized wet chemical
impregnation to synthesize the thin ZrO<sub>2</sub> film through the
procedure of first spin-coating a zirconium ethoxide (Zr(OC<sub>2</sub>H<sub>5</sub>)<sub>4</sub>) precursor onto a SiO<sub>2</sub>/Si(100)
substrate at room temperature followed by calcination at 773 K for
12 h. Scanning electron microscopy (SEM) investigations indicate that
highly porous “sponge-like nanostructures” were obtained
in this case. The second method was epitaxial growth of a ZrO<sub>2</sub>(111) film through vacuum evaporation of Zr metal onto Pt(111)
in 1 × 10<sup>–6</sup> Torr of oxygen at 550 K followed
by annealing at 1000 K. The structural analysis with low energy electron
diffraction (LEED) of this film exhibits good long-range ordering.
It has been found that Au forms smaller particles on the porous ZrO<sub>2</sub> film as compared to those on the ordered ZrO<sub>2</sub>(111)
film at a given coverage. Thermal annealing experiments demonstrate
that Au particles are more thermally stable on the porous ZrO<sub>2</sub> surface than on the ZrO<sub>2</sub>(111) surface, although
on both surfaces, Au particles experience significant sintering at
elevated temperatures. In addition, by annealing the surfaces to 1100
K, Au particles desorb completely from ZrO<sub>2</sub>(111) but not
from porous ZrO<sub>2</sub>. The enhanced thermal stability for Au
on porous ZrO<sub>2</sub> can be attributed to the stronger interaction
of the adsorbed Au with the defects and the hindered migration or
coalescence resulting from the porous structures
