IFISUR   23398
INSTITUTO DE FISICA DEL SUR
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Bonding analysis of Pd2H2 systems adsorbed on graphene layers
Autor/es:
I. LÓPEZ CORRAL, E. GERMÁN, M.A. VOLPE, G.P. BRIZUELA, A. JUAN
Lugar:
La Plata
Reunión:
Conferencia; Humboldt Kolleg International Conference on Physics (Argentina-Alemania); 2011
Institución organizadora:
UNLP
Resumen:
In this work we report a bonding study of the adsorption of Pd2H2 systems on a graphene layer, using the density-functional theory and the SIESTA code [1,2]. We modelled the graphene sheet by means of a periodically repeated tetragonal unit cell, consisting of 24 C atoms in a plane honeycomb structure. Different adsorption sites on the carbon surface and both molecular as dissociative Pd2H2 coordination structures were considered. Our results show that the adsorption of the Pd2 dimer in a parallel approach respect to the graphene sheet is only 260 meV stronger than the adsorption of two individual Pd atoms located on remote sites, so palladium shows less preference to cluster than other transition metals adsorbed on carbon surfaces [3]. According to previous studies [4], we verified by means of Mulliken analysis that the C-Pd bonding involves a small donation from Pd 4d to C 2s orbitals and a higher back-donation from C 2p to Pd 5s orbitals. In presence of dihydrogen, both dissociative (PdH)2 and not dissociative Pd2(H2) systems are originated, developing similar binding energies for the bridge (at the midpoint of a C-C bond) or top (above a C atom) sites. On the contrary, adsorbed single Pd atoms originate preferably a molecular Pd(H2) structure, with a relaxed but not dissociated H-H bond [5]. As a result of the support interaction, Pd-Pd and Pd-H bonds are elongated regarding the un-supported Pd2H2 coordination structures, and the C-Pd interactions results weakened with respect to the free-H graphene/Pd2 system, reducing both donation from Pd 4d to C 2s orbitals as back-donation from C 2p to Pd 5s orbitals.