The electron paramagnetic resonance (EPR) spectroscopy was used to study the adsorption of air at room temperature on Au/CeO2 solids prepared by impregnating gold on cerium oxide. Two EPR signals, P and M, where then identified. The P signal having g(parallel to)>g(perpendicular to), was mainly present on the EPR spectra recorded at room temperature and -196 degrees C for solids with low gold content (Au less than 1.25 wt.%). This signal was attributed to O-2(-) species strongly attached to the CeO2 surface. The M signal with g(perpendicular to) > g(parallel to) was only observed at -196 degrees C. Both P and M signals were obtained for solids with low gold content while M alone was present for solids with high gold content (2.5 wt.% and above). The M signal was also obtained even when air was adsorbed at -196 degrees C on the solids. O-17-enriched molecular oxygen adsorption allowed the identification of the M signal as being the result of O-2(-) species. These species are wealdy interacting with the surface of ceria containing Cl- ions probably present in CeOCl micro-phase. The O-2(-) species responsible of the P signal are formed in solids containing gold nanoparticles and are efficient in the catalytic total oxidation of propylene. (C) 2015 Elsevier B.V. All rights reserved.