(1) - Centro de Investigação em Química, Departamento de Química da Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal

(2) - Departament de Qu�mica F�sica i Centre de Recerca en Qu�mica Te�rica, Universitat de Barcelona, C/Mart� i Franqu�s, E-08028 Barcelona, Spain

The interaction of small Pdn clusters (n=3,4) with the relaxed Al-terminated alpha-Al2O3(0001) surface was investigated using both an embedded cluster model and a first principles hybrid gradient-corrected density functional approach. To model the infinite oxide surface, two different finite cluster models were considered. Both clusters are of semi-spherical shape being one of them centered on an aluminum atom and the other on an oxygen atom. The first model, consists of 23 atoms, 8 Al and 15 O, embedded in 18 Total Ion Potentials (TIPs) and 2354 Point Charges (PCs) with values of +3|e| and -2|e| for cations and anions respectively. The second model contains 29 atoms, 7 Al and 22 O, which are embedded in 17 TIPs and 2794 PCs. In order to obtain knowledge about the influence of the oxide support on the catalytic properties of the palladium surface, calculations were also performed for gas-phase Pdn clusters. The results obtained in the present work will be compared with previous data computed for the interaction of a single palladium atom with the alpha-Al2O3(0001) surface. Also, the effect of the metal-support interaction in the properties of the metal catalyst will be discussed.