Au/TiO2 catalysts for low-temperature CO oxidation exhibit dual-perimeter-sites catalysis in which CO molecules adsorbed at both Au and TiO2 surfaces diffuse to Au/TiO2 perimeters and are oxidized into CO2. Via a comprehensive in situ DRIFTS study of CO adsorption and oxidation on Au/TiO2 catalysts with different TiO2 morphologies predominantly exposing {0 0 1}, {1 0 0}, and {1 0 1} facets, we report that such dual-perimeter-sites catalysis depends sensitively on TiO2 morphology and facets. Adsorbed CO molecules remain stable on TiO2 surfaces up to 223 K. The migration of CO molecules from TiO2 to Au-TiO2 perimeter sites depends on the catalytic activity of Au-TiO2 perimeter sites. Dual-perimeter sites catalysis occurs within Au/TiO2{1 0 0} and Au/TiO2{1 0 1} catalysts with catalytically active Au-TiO2 perimeter sites that exhibit large coverage gradients between CO molecules adsorbed at Ti and Au sites, facilitating the migration of CO molecules from TiO2 to the Au-TiO2 perimeter sites, but seldom within Au/TiO2{0 0 1} catalysts with catalytically inactive Au-TiO2 perimeter sites that exhibits few coverage gradients between CO molecules adsorbed at Ti and Au sites. These results provide novel insights into the structure-activity relationship in Au/TiO2 catalysts for low-temperature CO oxidation. (C) 2018 Elsevier Inc. All rights reserved.