O-2 adsorption and CO oxidation on a Au/rutile TiO2(1 1 0) catalyst have been examined by DFT in order to define the extent of the reactive perimeter zone. O-2 is found to adsorb on the fivefold coordinated Ti sites that are away from the perimeter as well as on those next to the perimeter. Both O-2 show similar reactivity toward a gaseous CO. CO oxidation still occurs predominantly at the perimeter because O-2 adsorption is strongest at the perimeter Ti site and because CO is activated on Au through back donation. (C) 2014 Elsevier B.V. All rights reserved.