It is demonstrated that CO dissociates on a potassium-modified Cu(115) surface at 125 K. The dissociation process is conditioned by both the presence of steps and an alkali metal coverage in the range of 0.4 < theta(K), < 1 ML, Carbonate is formed at 220 K via the Boudouard process CO + CO --> CO2 + C and reaction with oxygen. Further annealing to 470 K results in decomposition of the carbonate with graphitic C and O atoms left on the surface. The evidence comes from synchrotron radiation-based measurements of the valence band electron energy distributions and high-resolution measurements of the K, C, and O core levels.