Effect of surface structure on the reactivity of yttria-stabilized zirconia

Catalysts involving metal oxide surfaces have been shown lately to exhibit reactivity that depends strongly on the surface structure. Additionally, the reactivity of metals supported on oxide surfaces might also be affected by the surface structure. The structure sensitivity of oxygenate molecules, such as carboxylic acids, aldehydes, and alcohols on ZrO$\sb2$ single crystals was studied by temperature programmed desorption (TPD) and high-resolution electron energy-loss spectroscopy (HREELS). It was effectively demonstrated that the concentration of surface defects, the coordination of surface ions and their relative positions on the surface can affect the reactivity and selectivity of oxygenate molecules on ZrO$\sb2$. The growth and thermal stability of Pt deposited on ZrO$\sb2(100)$ was also studied by HREELS. These studies indicated that Pt grows in a layer-by-layer mode on ZrO$\sb2$ at room temperature, but heating to higher temperature leads to agglomeration of the Pt films into particles. This technique proved to be useful in probing both the growth mode and stability of the metal overlayers, as well as the electronic properties of the surface. The reactivity of CO and $\rm C\sb2H\sb4$ was studied on Pt films and Pt particles on ZrO$\sb2$(100). HREELS revealed two species of CO on Pt particles, not observed on Pt films, one bonded at the steps of the Pt particles and another bonded between the Pt and the oxide substrate. This is the first report of such species in UHV studies of metal supported on oxide substrates. Another species, $\pi$-bonded-$\rm C\sb2H\sb4$ was observed upon low temperature $\rm C\sb2H\sb4$ adsorption on defects and steps of the Pt surfaces. These findings support the view that the local surface structure and not electronic effects is the determining factor for the reactivity of metals supported on oxides