First-principles theoretical investigations on the oxidation of ${\text{Pd}}_n$ $\left(n=1–7,10\right)$ clusters deposited on alumina/NiAl(110) have been carried out using a gradient-corrected density-functional approach. Our studies indicate that the free ${\text{Pd}}_n$ clusters are compact and maintain their compact structures when deposited on the surface, undergoing only small relaxations of the Pd-Pd distance. The clusters bind to the surface via a pair of Pd atoms and with a binding energy of around 1.0 eV. Studies of oxidation through an ${\text{O}}_2$ molecule show that ${\text{O}}_2$ occupies sites closer to the surface for ${\text{Pd}}_1$, ${\text{Pd}}_4$, ${\text{Pd}}_5$, and ${\text{Pd}}_6$ while, in other cases, the binding is highest to Pd atoms farther from the surface. An analysis of the charge gained by the ${\text{O}}_2$ molecule upon absorption shows that, while ${\text{O}}_2$ always gains charge, the amount of charge contributed by the ${\text{Pd}}_n$ cluster or the surface can vary significantly. In particular, in the case of ${\text{Pd}}_4$, only a small charge is donated by the cluster, thus accounting for the recently observed lack of shift in the x-ray photoelectron spectroscopy levels.

• Received 11 June 2010

DOI:https://doi.org/10.1103/PhysRevB.82.085428