CO2 adsorption on Na precovered Cr2O3(0 0 0 1)

CO2 adsorption and reaction on Cr2O3(0 0 0 1) is considerably modified by the presence of Na on the surface. Depending on Na coverage, different modes of interaction and reaction have been observed. At low coverage Na adsorbs by transferring an electron to the Cr2O3(0 0 0 1) surface. In this case, the formation of bent CO2− (carboxylate) can be observed similar to what was observed for the clean Cr2O3(0 0 0 1) surface [see Surf. Sci. 421 (1999) 176]. Distinct differences with respect to physisorbed CO2 are identified. CO2 desorbs as an intact molecule from the Na-covered surface at temperatures higher than that found for the clean surface. NaCO2 salts form and also Na2CO3 can be observed. Carbonate forms via disproportionation of two CO2 molecules into carbonate and CO with the latter being released into the gas phase. The intermediate formation of an oxalate species, its geometry on the surface, and CO2−•CO2 solvation are discussed.