Bimetallic MnO2-supported catalysts for selective reduction of NO with NH3. Operando IR studies

• The promotion with CeO x lead to an improvement in catalytic activity. • MnCe showed a higher O α concentration which promotes the oxidation of NO to NO 2. • The higher catalytic activity of Ce promoted catalyst may be related to its capacity to adsorb NO x even in presence of water. • The incorporation of FeO x decreased NO x conversion in presence of water. Bimetallic shaped catalysts were prepared by wet equilibrium impregnation. MnO 2 was the main component and a second metal oxide (Co, Fe and Ce oxides) was added. The highest catalytic activity in the selective reduction of NO x with NH 3 of the Ce-promoted catalyst (88% of NO was converted at 170 °C) may be related to its capacity to adsorb NO x even in presence of water. It is demonstrated that NO adsorbs and oxidizes on CeO x and MnO x and then reacts with NH 3 via a Langmuir-Hinshelwood mechanism. However, in presence of water, the surface of Fe-promoted catalyst during NH 3 -SCR was only covered by NH 3 adsorbed species and NO x conversion was lower (65% of NO was converted at 170 °C). NO x adsorbed species were not observed, which suggests that the reaction of ammonia with gaseous NO x was much faster than that of nitrites/nitrates formation. Elay-Riedel seems to be the predominant mechanism over this catalyst.