These concepts and mechanistic ideas were also applied to reactions on bimetallic catalysts. For a series of binary solid solutions containing one group 8 element (Ni, Pd or Pt) together with one of group I element (Cu, Ag or Au) and the binary alloys of iron, cobalt and nickel, the efficacy in multiple bond saturation or in dehydrogenation was suggested to largely depend on the number and the characteristics of the holes in the d-bands of the alloys . Later, electronic effects were discussed in a more local picture and the (enhanced) reactivity of bimetallic catalysts was associated with modifications of the electronic properties of a surface atom, which may represent the active site, due to interaction with different neighboring surface and subsurface atoms . In analogy to similar effects in coordination chemistry and homogeneous catalysis, where the state and catalytic behavior of the metal center are strongly influenced by its ligands, these effects were termed as electronic ligand effects. These as well as strain effects, which reflect the effect of lattice distortions as compared to the natural lattice of the respective surface layer on the electronic structure , can lead to changes in the adsorption energy (see section 3.1) and thus to significant modifications in the reaction kinetics . Also for bimetallic catalysts, geometric effects were considered as an alternative important parameter and introduced as geometric ensemble effect, which describes the influence of the size/configuration of the active surface ensembles on the catalytic activity via their concentration .