New insights into MnCe(Ba)Ox/TiO2 composite oxide catalyst: Barium additive accelerated ammonia conversion

MnCeO x /TiO 2 has been widely used in selective catalytic reduction (SCR) of NO x at low temperature. However, it is often poisoned in the presence of water vapor and sulfur dioxide . In this work, the promotion mechanism of Ba modification was investigated. Results show that the doped BaO reacts with CeO 2 and forms BaCeO 3 . This unique perovskite structure of BaCeO 3 significantly enhances NO oxidation and NH 3 activation of MnCeO x /TiO 2 catalyst so that the NO conversion and the resistances to SO 2 improve. It is found that Ba species obviously promotes the NO adsorption ability and improve the redox properties of MnCeO x /TiO 2 catalyst. While the acid properties of the catalyst are inhibited by Ba modification and among which Lewis acid sites are dominant for both MnCeO x /TiO 2 and MnCe(Ba)O x /TiO 2 catalysts. Furthermore, in situ DRIFT experiments reveal that the NO reduction upon MnCeO x /TiO 2 and MnCe(Ba)O x /TiO 2 catalysts follows both E-R and L-H mechanisms, in which L-H is preferred. Ba species enhances the formation of active nitrate species, which accelerates the NO reduction through L-H mechanism. It is interesting that although Ba species weakens the NH 3 adsorption, it induces the ammonia conversion to coordination ammonia, which in turn accelerates the catalytic reaction .