Low-temperature selective catalytic reduction of NO with NH₃ over iron and manganese oxides supported on titania

A series of catalysts of manganese oxide supported on TiO₂ and iron-manganese oxide supported on TiO₂ with different amounts of manganese and iron were studied for low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. It was found that the addition of iron oxide not only increased the NO conversion and N₂ selectivity but also increased the resistance to H₂O and SO₂. The Fe-Mn/TiO₂ catalysts yield high activities and high N₂ product selectivity. The N₂O product selectivity increased with the amount of MnO_x as well as temperature. Crystalline phase of MnO_x was present at ≥ 15% Mn on TiO ₂, and the amount increased with Mn content. In addition, SO ₂ and H₂O decreased the activities only slightly, while such effect was reversible, The Fe-Mn/TiO₂ with Mn/Fe = 1 showed the highest activity. The results showed that this catalyst yielded nearly 100% NO conversion at 120°C at a space velocity of 15,000 h^-1. The effect of oxygen was also studied. Reversible transient behaviors similar to that on other oxide catalysts, including vanadia and chromia, were observed for the Fe-Mn/TiO₂ catalyst.