THE GROWTH AND PROPERTIES OF PD AND PT ON AL2O3/NIAL(110)

Small metal particles have strongly size-dependent properties, which - in the case of supported particles - are also influenced by the particle substrate interaction. We have investigated such effects for Pd deposited on a thin alumina film grown on NiAl(110) by probing the adsorption behaviour of CO. Structure and size of the metal islands were varied by employing different substrate temperatures during evaporation. We found that at 90 K small, disordered aggregates are formed, whereas deposition at 300 K results in larger crystallites with (111) facets. The CO thermal desorption spectra show a size-dependent behaviour which can be attributed to a higher degree of CO coordination with decreasing particle size. The results are compared with the corresponding behaviour of Pt. In contrast to Pd, Pt leads to a strong interaction with the substrate at 300 K. This gives rise to a desorption feature of CO in a temperature range which is typical for transition metal oxides.