H2 INTERACTION WITH BIMETALLIC DIMERS SUPPORTED ON THE MgO(100) SURFACE: A DFT CLUSTER MODEL STUDY

The interaction between the H2 molecule and the PdAg, PdAu, PtAg and PtAu bimetallic dimers deposited on the MgO(100) surface is investigated using density functional theory (DFT). The bimetallic dimers, whose molecular axes are considered to be perpendicular to the support surface, are adsorbed on top of an oxygen atom. Within this adsorption mode, the dimers prefer the orientation in which their Pd or Pt end is closer to the oxygen atom. The Ag and Au ends of the MgO-supported dimers capture the H2 molecule with small exoenergetic effects. The spontaneous dissociation of H2 on these ends does not occur. Thus, the MgO support decreases the ability of the dimers to adsorb and dissociate the H2 molecule. From a catalytic viewpoint, it means that the activity of small bimetallic clusters toward the dissociative adsorption of H2 is reduced when they are arranged on MgO. On the other hand, the results of our calculations show that the presence of the MgO support strengthens the binding of H atoms inside the PdAu, PtAg and PtAu dimers.