Moving on to CO adsorption on PtAg/Pt and PdAg/Pd Based on rather similar observations for CO adsorption on Pt [127], they explained this by a simultaneous population and de-population of bridge and on-top sites during CO adsorption / desorption. The only difference between their results and the above theoretical prediction, the absence of COad on threefold sites on Pt3 and larger ensembles at low COad coverages in their measurements, may be due to either the slightly lower adsorption energy on these sites (see Figure )