An EPR study of physi- and chemisorption of NO on MgO: Effect of outgassing temperature and nature of surface sites

The interaction of NO molecules with the surface of MgO has been studied by EPR as a function of outgassing temperature. Two different types of paramagnetic species are identified by EPR: physisorbed NO and chemisorbed NO22−. They are formed upon specific adsorption of NO on Lewis acidic Mg2+ and basic O2− sites, respectively. The concentration of NO and NO22− radicals depends on the outgassing temperature of MgO reaching a maximum at 1073 K. FT-IR measurements suggest that sites liberated upon thermal outgassing by removal of OH and carbonate groups adsorbed on MgO play a significant role in the increase of the concentrations of NO and NO22− radicals. The latter are possibly formed on low coordinated oxide ions close to cationic vacancies or O4C2− of monoatomic step and O3C2− from kinks and divacancies.