Density functional theory studies of sulfur binding on Pd, Cu and Ag and their alloys

We present gradient corrected density functional theory calculations on the adsorption of sulfur on pure Pd(1 1 1), Cu(1 1 1) and Ag(1 1 1) surfaces as well as on PdCu3(1 1 1), Pd3Cu(1 1 1), PdCu(1 1 0), PdAg3(1 1 1) and Pd3Ag(1 1 1) surfaces. Sulfur forms strong bonds with all the surfaces and favors hollow sites in every case. The binding energies on the pure metals show considerable variation and follow the trend: Ebind(Pd(1 1 1))>Ebind(Cu(1 1 1))>Ebind(Ag(1 1 1)). On the alloy surfaces, the adsorption energies in general are weaker in comparison to adsorption on the Pd(1 1 1) surface but the reduction in binding is not large. The strong interaction of sulfur with these surfaces arises from rehybridization of the p-states of the adsorbate with the substrate sp- and d-bands. We confirm that there is nearly a linear correlation between the binding energies of S on similar adsorption sites and the d-band center of surface atoms whose structure remain close to their bulk-truncated position.