Adsorbed Oxygen Species Formed by the Decomposition of N2O on Li/MgO Catalysts

Article abstract of DOI:10.1246/bcsj.66.2467

A considerable amount of adsorbed oxygen species were produced by the decomposition of N2O on Li/MgO.The amount of the oxygen species greatly increases by Li(I)-doping on MgO.Over 0.7 wtpercent Li/MgO, the amount of the oxygen species formed was 10.67 μmol m^-2.The temperature-programmed desorption of the oxygen species revealed that two types of adsorbed oxygen species were present on Li/MgO; one (α-oxygen species) desorbed in proportion to the second order in the amount of the adsorbed species with an activation energy of 141 kJ mol^-1, giving a peak (α-oxygen peak) at 673-693 K; the other (β-oxygen species) desorbed in proportion to the first order in the amount of the adsorbed species with an activation energy of 219 kJ mol^-1, giving a peak (β-oxygen peak) at 753-768 K.A weak α-oxygen peak occurred on MgO and no β-oxygen peak was discerned.On Li/MgO, a β-oxygen peak appeared along with an α-oxygen peak.At higher Li-loadings the β-oxygen peak was more intense than the α-oxygen peak.The sites for these oxygen species were suggested to be derived by the addition of Li(I) on MgO.It was suggested that the α-oxygen species were present at the surface sites on higher index faces of MgO, whereas the β-oxygen species were present at oxygen vacancies in the vicinity of Li(I) substituting for Mg(II).The hydrolysis of these adsorbed oxygen species yielded an appreciable amount of H2O2, suggesting that these species were primarilly present as surface peroxide on MgO and Li/MgO.