N2O decomposition on MgO and Li/MgO catalysts: A quantum chemical study

Ab initio embedded cluster model calculations have been performed to study the decomposition of N2O on MgO and Li/MgO catalysts. The following has bee n found. (i) On MgO(001) terrace atomic oxygen is adsorbed on top of the O- 5c anions, while on corners or steps the preferable mode is for atomic oxyg en to bridge over the low-coordinated O-XC-Mg-YC (X, Y = 3, 4) ion pairs. T he adsorption of atomic oxygen leads to the formation of a peroxide ion. (i i) N2O decomposition over a five-coordinate terrace anion would be possible , while the defective O-XC-Mg-YC (X, Y = 3, 4) ion pairs are more active to decompose N2O. The activity of the Q(XC)-Mg-YC (X, Y = 3, 4) ion pairs tow ard N2O decomposition could be assigned in the order O-3C-Mg-3C > O-4C-Mg-3 C > O-3C-Mg-4C > O-4C-Mg-4C (iii) When the MgO catalyst is doped with Li, t he so-called [Li+O-] centers are found to be active for decomposing N2O, an d the decomposition of N2O on the active [Li+O-] center leads to the format ion of the superoxide anion. This accounts for the higher reactivity and se lectivity of the Li/MgO catalyst.