Characterization of the Pd/a-Al2O3 supported cluster system

Palladium deposits supported on amorphous alumina were prepared in ultrahigh vacuum and studied using transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and energy loss spectroscopy (ELS). The growth of clusters with deposition time was followed using TEM. The XPS, AES, and TEM results support a consistent model for the distribution of palladium on the alumina substrate, with the amount of material within the clusters accounting for the majority of the palladium deposited. The combined results of XPS, ELS, and TEM indicate that the deposit growth with deposition time can be tentatively separated into the following size regimes: monolayer islands, ‘‘small’’ clusters and metallic three-dimensional clusters. The size-dependent XPS Pd 3d binding energy shifts are analyzed within the initial-state-final-state framework. Component fitting of the Pd 3d spectra is consistent with assigning one of the components to the layer of interfacial Pd atoms.