O2-probe EPR as a method for characterization of surface oxygen vacancies in ceria-based catalysts

Catalytic activity of ceria-based systems is essentially related to the oxygen storage/release characteristics of the surface and, therefore, to the properties of the oxygen vacancies generated upon reduction of CeO2. EPR analysis of the superoxide species formed upon low temperature oxygen chemisorption on this type of systems is shown to be a very powerful method to characterize such defects. The present work revises results mainly obtained in the authors’ laboratory on this topic and shows the main physicochemical properties of such superoxide species. Situations of practical interest in the field of heterogeneous catalysis are analysed. These include the analysis of defects formed on pure CeO2, as well as their chemical modification by NO chemisorption or in the presence of chlorine impurities, typically present in supported metal catalysts. Additionally, the characterization of two-dimensional ceria structures in alumina-supported ceria systems with high practical interest is shown to be uniquely provided by this EPR-based method.