Semihydrogenation of Acetylene on Al5Co2 Surfaces

Density functional theory calculations are used to investigate the catalytic properties of the low-index surfaces of Al5Co2 toward the semihydrogenation of acetylene. Adsorption energies of species involved in the reaction (H, C2H2, C2H3, and C2H4) are calculated on the (001), (100), and (2 (1) over bar0) 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 C2Hx are established. Surface activity has been investigated on the (2 (1) over bar0) 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.