SUPEROXIDE (O2-) ON THE SURFACE OF HEAT-TREATED CERIA - INTERMEDIATES IN THE REVERSIBLE OXYGEN TO OXIDE TRANSFORMATION

Powder X-ray diffraction (XRD) and electron spin resonance (ESR) studies were employed for the study of oxygen interaction with nonstoichiometric ceria CeO2 --> CeO2-x. The crystal structure of CeO2 is maintained during heat treatment in vacuo from 573 to 1073 K. Oxygen adsorption yields ESR signals for three species believed to all be due to O2- adsorbed at different surface sites. Studies of temperature dependence, reactivity, and stability suggested that two side-on-bonded O2- species were formed along with an end-on-bonded species probably inserted into a surface oxygen vacancy. This end-on-bonded species behaves as an intermediate in the pathway to re-formation of a lattice oxide dianion.