Making a noble metal of Pd

We present theoretical and experimental data concerning the possibility of inducing in Pd properties characteristic of a noble metal. A free-standing Pd( 100) monolayer expanded to the lattice constant of 3.30 angstrom exhibits an atomic-like electronic structure, having its d-valence states almost full, like the noble metals Cu, Ag or Au. To prevent de-population of the d-states, we deposit the Pd ML on a Nb(100) substrate passivated by a pseudomorphic S monolayer. The weak interaction with the S-capped Nb( 100) surface causes the centre of the d-states of the Pd monolayer to lie much closer to the Fermi level than in bulk Pd. As a result, the weakly bonded Pd monolayer becomes more reactive than bulk Pd. However, when Pd is deposited directly on the Nb( 100) surface, the strong, direct bonds between Pd and Nb push the d-band centre of the monolayer toward lower binding energies, resulting in Pd reactivity comparable to that of the noble metal Ag.