Adsorption, Diffusion, and Dissociation of H2S on Fe(100) from First Principles

We employ spin-polarized periodic density functional theory (DFT) to characterize H 2 S and HS adsorption, diffusion, and dissociation on the Fe(100) surface. We investigate the site preference of H 2 S, HS, and S on Fe(100). H 2 S is predicted to weakly adsorb on hollow, bridge, and on-top sites of Fe(100), with the bridge site preferred. The diffusion barrier from the bridge site to the next most stable on-top site is predicted to be small (∼0.15 eV). In contrast to H 2 S, HS is predicted to be strongly chemisorbed on Fe(100), with the S atom in the hollow site and the HS bond oriented perpendicular to the surface, due to charge transfer from the surface to S p-orbitals. Isolated S atoms also are predicted to bind strongly to the hollow sites of Fe(100), with the bridge site found to be a transition state for S hopping between neighboring hollow sites. The minimum energy paths for H 2 S and HS dehydrogenation involve rotating an H atom toward a nearby surface Fe atom, with the S−H bonds breaking on the top of only one Fe atom. The barriers to break the first and second S−H bonds in H 2 S are low and about the same, ∼0.25 eV, suggesting deposition of S on Fe(100) via H 2 S is kinetically and thermodynamically facile, consistent with experiments.