Semihydrogenation of Acetylene on Al₅Co₂ Surfaces

Density functional theory calculations are used to investigate the catalytic properties of the low-index surfaces of Al 5 Co 2 toward the semihydrogenation of acetylene. Adsorption energies of species involved in the reaction (H, C 2 H 2, C 2 H 3, and C 2 H 4 ) are calculated on the (001), (100), and (21̅0) surfaces. Hydrogen adsorption sites are found to be stabilized by subsurface cobalt atoms, showing an electron donor character. Scaling relations between the adsorption energies of C 2 H x are established. Surface activity has been investigated on the (21̅0) surface. A possible reaction path for the semihydrogenation of acetylene is proposed using nudged elastic band calculations, starting from a 3-fold adsorption site made of three aluminum atoms. The corresponding activation energy of the rate-controlling step is calculated to be 60 kJ mol –1 . The activation energy of the rate-controlling step toward total hydrogenation is evaluated to be 106 kJ mol –1, thus suggesting a selective surface for catalysis.