Quantum chemical DFT study of molecular adsorption of H2S on clean and chemically modified Au(1 1 0) surfaces

Abstract

The non-dissociative adsorption of H2S on Au(110) and the coadsorption with SH, S and H have been examined by periodic density functional theory (DFT) to indirectly give useful information about the associated surface reactivity. For bare surfaces, the enthalpy calculations indicate that energetically favored adsorption structures are generated at low to medium coverage. Each coadsorbate does not appreciably perturb the binding configuration but does promote the adsorption. With the aid of the calculated electron density differences, the trends can be rationalized in the context that the surface H2S constitutes hydrogen bonding only with the preadsorbed SH and S species. Unexpectedly, there is a net charge transfer from the seemingly electronegative H2S towards the metal surface, which is far from chemical intuition. As for the experimental adsorption enthalpy, comparatively strong values of it are here affirmed to be related to the case in which some molecules have decomposed at Au(110). Furthermore, only on the S-modified surface do the predicted vibrational frequencies of H2S agree with the published HREELS spectra, suggesting that the dissociation leaves, instead of the previously proposed SH fragment, atomic sulfur on Au(110) at low temperatures.