Gradient-corrected density functional theory (GC-DFT) calculations have been performed for molecular hydrogen, carbon monoxide and the metal dimers Pt-Pt, Pt-Ni, and Pt-Ru. The dissociative adsorption of molecular hydrogen on these metal dimers has been modelled. Derived potential energy surfaces for the dissociation of molecular hydrogen on these dimers are presented. Furthermore, the interaction with carbon monoxide has been studied. Here we find that Pt 2 binds CO significantly stronger than Pt-Ni and Pt-Ru. We present equilibrium geometries, calculated binding energies, Mulliken charge distributions, and orbital energies. Our results correlate well with our experimental studies of the hydrogen electro-oxidation reaction in a proton-exchange fuel cell where the fuel to the anode (Pt/Pt alloy on carbon electrode) is hydrogen, prepared by reforming of methane, which contains trace amounts of carbon monoxide.