New insight on N2O formation over MnOx/TiO2 catalysts for selective catalytic reduction of NOx with NH3

High N 2 O selectivity of MnO x -TiO 2 catalyst hinders its development in ammonia selective catalytic reduction (NH 3 -SCR) of NO x . Herein, a series of MnO x -TiO 2 catalyst with different Mn/Ti ratio were prepared by wet-impregnation method to study the N 2 O formation during ammonia selective catalytic reduction (NH 3 -SCR) of NO x from the perspective of catalyst. It is found that MnO x and TiO 2 species are the mainly redox and acid sites for the NH 3 -SCR denitration reaction over MnO x -TiO 2 catalyst, respectively. As the Mn/Ti ratio increases, MnO x species layer expanded on TiO 2 support, leading to increase of redox sites but decrease of surface acid sites. These changes contribute to the occurrence of the no-selective oxidation of NH 3 on MnO x species and the over-activation of NH 3 at Mn-Ti interface, resulting in the formation of N 2 O via the route of 2NH 3  + 2O 2  → N 2 O + 3H 2 O and 4NO + 4NH 3  + 3O 2  → 4N 2 O + 6H 2 O, respectively. Through this work, it can be speculated that both improving MnO x dispersion and increasing surface acidity of catalyst are feasible strategy for suppressing the N 2 O formation on MnO x -TiO 2 .