As in section 3.2.1, we also evaluated the CO adsorption energies at similar or comparable sites in the presence of O-vacancies in vacancy clusters aside the Ru nanorod, starting from a vacancy on site 1i in the 1VO system and proceeding to site 17i in the 2VO system, site 18i in the 3VO system, and finally to site 14i in the 4VO system. These sites were chosen because they are adjacent to each other, with an increasing distance from the Ru nanorod. Figure illustrates the CO adsorption energies at the aforementioned sites in the 1VO, 2VO, 3VO, and 4VO systems, along with the fully oxidized Ru/ZrO2 system denoted as 0VO. Note that during optimization, CO adsorbed at the edge site of the top layer systems shifts to the hollow site formed by the Ru-7a, Ru-8a, and Ru-5a atoms in the 2VO and 3VO systems (Table ). Similarly, upon adsorption at the interface (i) site (Ru-1a, Ru-5a), CO relaxes to the threefold hollow site formed by the Ru-1a, Ru-4a and Ru-5a atoms for the 3VO and 4VO systems.