For both adsorption sites there are pronounced changes only in the presence of an O-vacancy on the (ii) site. For CO adsorption on the interface (i) site, this is mainly a CO induced charge transfer from support to the Ru nanorod, while the charge change on the CO is similar to that in the other systems. For CO adsorption on the interface (ii) site, in contrast, we find a considerable charge transfer from the support both to the Ru nanorod and to the adsorbed CO, which both become more negative. Hence, the contributions from the charge transfer to the increase in CO adsorption energy on the two interface sites in the presence of an O-vacancy on the (ii) site are different, although it involves in both cases a charge transfer from the support upon CO adsorption, once to the Ru nanorod and once to both Ru nanorod and CO.