The role of preadsorbed sulphur and oxygen in O2 dissociation on Pd(1 0 0)

We have performed a density functional study for the poisoning of oxidation reaction of the Pd(1 0 0) surface by preadsorbed sulphur and oxygen. We find that the mechanism for this effect is due to (i) the physical blocking of the reactive sites, (ii) Coulombic charging caused repulsion between the incoming molecule and the poison, and (iii) the Pauli repulsion caused by the mixing of the electronic states of O2 and the preadsorbents. The strength of the mechanisms (ii) and (iii) vary between the preadsorbed species. In addition, we have studied the effect of sulphur and oxygen coverage dependence on the poisoning of the dissociation of O2. It is also observed that preadsorbed sulphur affects the electronic structure of the metal atoms only locally and has therefore only a small effect on molecules adsorbing to the clean parts of the surface.