In a similar way, we evaluated changes in the CO adsorption energy on the different sites induced by the presence of O-vacancies aside the Ru nanorod, without direct contact to it (see section 3.1.2). Here we tested the influence of O-vacancies at sites 16i, 18i and 13i, which because of their different distances to the closest Ru atom of 4 Å, 6 Å and 7.3 Å (see Figure ) can be considered as representative for the sites in the first row (sites 16i, 18i) and second row (13i-15i) (Figure ). The CO adsorption energies resulting for adsorption on the fully oxidized Ru/ZrO2 system (grey bars) and for adsorption on the Ru/ZrO2-x systems with a single O-vacancy are displayed in Figure . Similar to the results for individual O-vacancies underneath the Ru nanorod (Figure ), we find essentially no changes for CO adsorption on the top layer. For adsorption at the middle layer site, which is generally slightly stronger again than on the top layer sites, CO is mostly adsorbed on the Ru-5a atom. Only for the system with the O-vacancy at the 16i site it spontaneously migrates to the hollow site formed by the Ru-1a, Ru-2a, and Ru-5a atoms (Table ) (hatched bar in Figure ). This site is identical with the interface (i) adsorption site. The about constant CO adsorption energy on the fully oxidized system and for O-vacancies on the 18i and 13i sites agrees fully with the essentially constant charge on the Ru adsorption site (Ru-5a atom) (Table ). For the O-vacancy at the 16i site, where the charge on the Ru adsorption site, in particular on the Ru-2a atom, is considerably more negative (Figure ), the CO adsorption energy is significantly higher, as would be expected if there is a correlation between Ru charge state and CO adsorption energy. In this case, CO interacts also directly with the support, in particular with the partly reduced 2Zr ion adjacent to the O-vacancy, and the electron transfer from the support to the CO molecule further strengthens the interaction between CO and the model catalyst (see Figure and Tables and). This is reflected also by the decrease of the distance between the 2Zr ion and the O atom of the CO molecule, from 2.52 Å for the fully oxidized system to 2.17 Å for the vacancy at the 16i site (13i: 2.37 Å, 18i: 2.40 Å) (Table ). For the other systems, this charge transfer is less pronounced. The stronger CO adsorption energy results mainly from an increase of the CO binding energy, while contributions from the deformation and interface energies largely cancel out (Figure ).