Density Functional Theory Study of the Oxygen Chemistry and NO Oxidation Mechanism on Low-Index Surfaces of SmMn2O5 Mullite

SmMn2O5 mullite has recently been reported to be a promising alternative to traditional Pt-based catalysts for environmental and energy applications. By performing density functional theory calculations, we have systematically investigated lattice oxygen reactivity and oxygen adsorption/dissociation/migration behaviors on low-index surfaces of SmMn2O5 mullite with different terminations. On the basis of the oxygen chemistry and thermodynamic stability of different facets, we conclude that (100)3+, (010)4+, and (001)4+ are reactive toward NO oxidation via either the Mars van Krevelen (MvK) or Eley–Rideal (ER) mechanism. Concrete NO → NO2 reaction paths on these candidate mechanisms have also been calculated. Both the (010)4+ and (001)4+ surfaces presented desirable activities. Bridge MnO sites on (010)4+ surface are identified to be the most active for NO oxidation through the ER mechanism with the lowest barrier of ∼0.38 eV. We have also identified that on all active sites considered in the current study, the rate-determining step in NO → NO2 oxidation reaction is the NO2 desorption. Our study gives an insight into the mechanisms of NO oxidation on SmMn2O5 mullite at the atomic level and can be used to guide further improvement of its catalytic performance.