The storage of NO, NO/O-2-mixtures and NO2 on CeO2 and BaO/CeO2 was investigated by in situ DRIFT-spectroscopy. The NOx-storage capacity, as well as the kinetic and the mechanism of the NOx-storage process are influenced by the temperature and the BaO-loading as well as the oxygen partial pressure. The addition of oxygen into NO containing gas mixtures results in the oxidation of the stored nitrite to nitrate species. Adsorption of NO2 leads to in the formation of nitrite and nitrate species, where the nitrite species are completely oxidized to nitrate in the progress of storage.