Adsorption Properties of the o‑Al13Co4(100) Surface toward Molecules Involved in the Semihydrogenation of Acetylene

This paper presents the adsorption properties of the o-Al13Co4(100) surface toward molecules involved in the semihydrogenation of acetylene. The energetically favored adsorption sites of H, C2H2, C2H3, and C2H4 are determined thanks to ab initio density functional calculations. The surface model used for this study has been determined previously [Phys. Rev. B 2011, 84, 085411], using an approach combining both experimental observations and density functional theory calculations. We show that although the surface termination layer of o-Al13Co4(100) is a dense Al-rich layer, its adsorption properties are quite different from pure elemental Al surfaces, especially for atomic hydrogen adsorption (exothermic on o-Al13Co4(100) and endothermic on low index Al surfaces). The role of surface and subsurface cobalt atoms is investigated carefully. The electronic donor/acceptor character of subsurface cobalt atoms is shown to influence the adsorption properties. In particular, the subsurface cobalt atoms have a rather stabilizing effect on adsorption while the role of surface cobalt atoms located slightly below the mean position of the termination plane is moderately destabilizing. These atomic interactions ensure the isolation of a well-defined active site on the surface.