Mechanism of trace element adsorption on a clean and S precoated Pd(1 1 1) surface: Insight from density functional theory calculations

The surface reactions of arsenic, selenium, and mercury on clean and S precoated Pd(1 1 1) surfaces were studied with periodic slab models based on density functional theory. The results showed that AsH3, AsH2, and AsH prefer to adsorb on the Pd surface with an up orientation, while H2Se and SeH favor a parallel orientation. Both the AsH3 and H2Se molecules were easily dissociated into their respective atomic states on the Pd(1 1 1) surface. The first dehydrogenation is the limiting step. For the S precoated Pd surface, trace elements favor direct binding to the surface Pd atoms rather than the S atoms. The As atom was predicted to be stable at the whole S coverage range, whereas the Se and Hg atoms were found to be stable at S coverages of 1/9–3/4 and 1/4–3/4 ML, respectively. The cooperative effect of the M–Pd (M = As, Se, or Hg), M–S, and S–Pd bond strengths on the stability of the trace elements adsorbed on the S precoated Pd surface was discussed.