The catalytic properties toward CO combustion of an encapsulated cluster, V@Au-12(-), have been explored by means of plane-wave pseudopotential density-functional theory calculations. Single adsorption of both O-2 and CO as well as coadsorption have been considered. The adsorption energy for the O-2 molecule is about 0.3-0.4 eV which limits its use to low temperatures. However, in contrast to what happens for pure gold clusters, this system shows a remarkable capacity to bind a high number of oxygen molecules. Moreover, its icosahedral cluster is able to bind 12 CO molecules, since all of the gold atoms are available. The bond between the metal cluster and the oxygen molecule mainly arises from a charge transfer from the metal toward the pi(g) antibonding O-2 orbitals, while in the case of CO molecule, the classical sigma-donation pi-back-donation mechanism is observed. Finally, no coadsorption effects are found when both molecules are adsorbed, the interaction properties between the cluster and the substrates remain basically unaltered.