Density functional theory calculations are used to investigate the catalytic properties of the o-Al13Co4(100) surface toward the semihydrogenation of acetylene. The dissociation of the H-2 molecule is the key process in this case, since the surface termination does not contain protruding Co atoms, according to a combination of surface science studies and ab initio calculations. However, compared to the pure Al(100) and Al(111) surfaces, H-2 dissociation on o-Al13Co4(100) proceeds much easier, due to the presence of surface Co atoms slightly below the mean position of the termination plane. A possible mechanism for the hydrogenation is presented, highlighting the selectivity of the reaction on this Al-rich surface.