To probe the influence of O-vacancies on the CO adsorption energy, we calculated the CO Stimulated by the Blyholder model, we also evaluated the change in the charge state of the ZrO2 support, of the Ru nanorod and of the CO molecule upon CO adsorption, which provides information on the charge transfer to the CO molecule (see Figure ). Obviously, this is a considerable simplification of the Blyholder picture, where the charge transfer (donation) from metal d-states into the 2* orbital of the CO molecule in combination with backdonation from the 5 orbital of the CO molecule into metal states with appropriate symmetry is decisive, as the latter distinguishes between different metal states. It would allow even a considerable strengthening of the metal -CO bond with no net charge transfer, if the contributions from charge donation into the 2* orbital and from the 5 orbital compensate each other. Nevertheless, it would be interesting to see whether there is a correlation between charge on the Ru adsorption site (before CO adsorption), total charge transfer to the CO and CO adsorption energy. For adsorption sites involving more than one surface Ru atom, we used the mean value of the d-band centers of the individual Ru surface atoms involved in the bonding.