N₂O Decomposition on MgO and Li/MgO Catalysts: A Quantum Chemical Study

Abstract

Ab initio embedded cluster model calculations have been performed to study the decomposition of N2O on MgO and Li/MgO catalysts. The following has been found. (i) On MgO(001) terrace atomic oxygen is adsorbed on top of the O5c anions, while on corners or steps the preferable mode is for atomic oxygen to bridge over the low-coordinated OXC−MgYC (X, Y = 3, 4) ion pairs. The adsorption of atomic oxygen leads to the formation of a peroxide ion. (ii) N2O decomposition over a five-coordinate terrace anion would be possible, while the defective OXC−MgYC (X, Y = 3, 4) ion pairs are more active to decompose N2O. The activity of the OXC−MgYC (X, Y = 3, 4) ion pairs toward N2O decomposition could be assigned in the order O3C−Mg3C > O4C− Mg3C > O3C−Mg4C > O4C−Mg4C. (iii) When the MgO catalyst is doped with Li, the so-called [Li+O-] centers are found to be active for decomposing N2O, and the decomposition of N2O on the active [Li+O-] center leads to the formation of the superoxide anion. This accounts for the higher reactivity and selectivity of the Li/MgO catalyst.