Oxidation ofPdn(n=1–7,10)clusters supported on alumina/NiAl(110)

Abstract

First-principles theoretical investigations on the oxidation of ${\text{Pd}}_{n}$ $(n=1--7,\text{ }10)$ 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.