The catalytic oxidation of carbon monoxide to carbon dioxide by gold nanoclusters loaded onto cerium oxide supports is an important reaction that has been increasingly tailored for use in hydrogen fuel cells. It has been known that there are simultaneous mechanisms that involve coordination of both the dioxygen and carbon monoxide to the gold, as well as one in which the dioxygen is contributed in the form of lattice oxygen while the gold still coordinates the carbon monoxide. The latter has been shown to be the more potent, and it is for this reason that modulating the cerium oxide support is of vital interest. The present work provides compelling evidence that the rate-limiting step in this process is the coordination of the lattice oxygen. Exploratory studies of the control or this step via doping the cerium oxide support are also presented. (C) 2016 Elsevier B.V. All rights reserved.