Modification of structural and chemisorption properties of small palladiumclusters supported on the MgO(001) surface from density functional calculations

We have performed gradient corrected density functional calculations on Pd tetramers and pentamers deposited on the regular MgO(0 0 1) surface as well as on the chemisorption of CO molecules on such Pd clusters. These systems can be considered as models of supported metal catalysts on a fully dehydr oxylated MgO surface. The oxide surface has been represented by MgO cluster s embedded in total ion model potentials and an array of point charges. The geometrical structures of Pd, Pd-4, and Pd-5 supported on the MgO substrat e have been optimized partially and the corresponding electronic properties have been analyzed. Both two- and three-dimensional Pd clusters have been considered. Changes in the electronic structure of the clusters induced by interaction with the substrate have been analyzed by adsorbing a CO probe m olecule on free and supported Pd clusters. Perturbation of the metal cluste r due to interaction with the support, although not large, has two importan t consequences: a weakening of the metal-metal bonds which results in an el ongation of the Pd-Pd distances within the cluster, and a change in the pre ferred adsorption site. On the other hand, the geometrical and vibrational properties of the adsorption complexes CO-Pd/MgO and CO-Pd do not differ si gnificantly. (C) 2000 Elsevier Science B.V. All rights reserved.