For CO adsorption on the interface (ii) site, adsorption on the fully oxidized Ru/ZrO2 and on the 1VO system are comparable in strength to adsorption on the top layer terrace site. Here, we find an increase in charge, mostly on the Ru-2a atom, already when moving from the 0VO to the 1VO system (Figure ), while the bridge adsorption site (Ru-2a and Ru-6a) is maintained.