A DFT study of [H.sub.2] adsorption on [Pd.sub.n]/Sn[O.sub.2]

Hydrogen adsorption on palladium atoms pre-adsorbed on a tin oxide semiconductor has been studied and compared with [H.sub.2] adsorption on a bare Sn[O.sub.2]. By means of density functional theory calculations, the preferential number of Pd atoms and their geometry as well as the physisorption and chemisorption of [H.sub.2] is analyzed on these surfaces. Namely, bare stoichiometric Sn[O.sub.2] (110) and Pd-doped Sn[O.sub.2] (110) surface systems are considered. It is found that Pd atoms tend to form clusters composed of 5 atoms. When considering sites with a favorable adsorption energy (>0.10eV), these pre-adsorbed [Pd.sub.5] clusters increase the number of active sites for [H.sub.2] chemisorption from 5--in the case of the bare surface --to 16 for the same surface area. Bare Sn[O.sub.2] (110) surfaces also present 5 potential sites for physisorption while [Pd.sub.5]/Sn[O.sub.2] surface presents 10 potential physisorption sites when applying the same adsorption energy criterion. Although dissociative [H.sub.2] adsorption is energetically more favorable for bare Sn[O.sub.2] than for [Pd.sub.5]/Sn[O.sub.2], the molecular [H.sub.2] adsorption is slightly more favorable for the doped system.