EPR investigation of the nature of oxygen species present on the surface of gold impregnated cerium oxide

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.