Enhanced activity and N2 selectivity for manganese oxides catalysts modified with transition metals: Mechanism and N2O formation pathways.

Various transition metals were employed to enhance the catalytic performance and N 2 selectivity of Mn-based catalysts. The modification of Fe and Cu promoted the low-temperature activity, while the Al-modified catalyst displayed the highest N 2 selectivity close to 100 %. The characterization results proved that the content of O β and Mn4+ were increased after adding transition metals. N 2 selectivity experiments revealed that the reduction of NO to N 2 O and the oxidation of NH 3 to N 2 O did not occur. The product of NH 3 oxidation was only N 2. Combined with the results of the in-situ DRIFTS experiments, it was proposed that N 2 O was generated from the decomposition of NHNO and NH 4 NO 3 in the SCR reaction. The poor N 2 selectivity of the unmodified catalyst was related to the existence of inactive N 2 O 2 2- species on the surface, while the high content of active NH 2 - species on the Mn 0.1 Ho 0.005 Ce 0.015 Al 0.01 /TiO 2 catalyst enhanced its catalytic activity and N 2 selectivity. In addition, the results also revealed that only the E-R mechanism existed on the unmodified catalyst, while both the E-R and L-H mechanism were activated after the transition metal modification. The SCR reaction of NH 3 and NO proved to be the source of N 2 O. The activation of the L-H mechanism might play a key role in the improvement of activity and selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]