Surface-Subsurface Preference of S Species on Transition Metal Nanoparticles: A DFT Study

Sulfur is a well-known catalyst poison, particularly for catalysts based on transition metals. Herein, we studied the adsorption of sulfur species on small nanoparticles (~1 nm in size) of the face centered cubic (fcc) transition metals (Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) using density functional theory (DFT) modeling. At low sulfur coverage (one S atom per nanoparticle), sulfur preferentially occupies the surface hollow sites of the nanoparticles. At higher coverage, however, the subsurface diffusion of S in Ni, Pd, and Ag nanoparticles becomes energetically favorable with low activation energies. Among the considered metals, sulfur binds most strongly to Rh and Ir, and most weakly to Ag and Au. The present results shed light on the facility of S-poisoning on such metal nanoparticles, either by surface blocking or by underlying sulfurization of the metal.