Transition metal modified Mn-based catalysts for CO-SCR in the presence of excess oxygen

Abstract

The CO-SCR technology based on transition metal is of great significance for NOx removal in large-scale industrial production. However, excess oxygen usually hinders the deNOx reaction in the actual industrial process. In this paper, a series of Mn-based catalysts modified by transition metals (Fe, Ni, Cu) were prepared using the co-precipitation method, which aimed to obtain good CO-SCR performance under O2-rich condition. The results showed that the Cu-Mn2 sample exhibited excellent deNOx performance. Regardless of the presence or absence of oxygen, the NO conversion of Cu-Mn2 catalyst was remain about 60% and 95% at 350 and 400 ℃, respectively. Differently, the NO conversion of Fe-Mn2 catalyst significantly increased from approximately 10% to 61% at 400 ℃ after introducing oxygen, which proved that excess oxygen could promote the CO-SCR process over Fe-Mn2 sample. The varied physical and chemical properties of the prepared materials were thoroughly evaluated through BET, SEM, XRD, XPS and in situ DRIFTS technologies. The results demonstrated that perovskite α-Mn2O3, decahedral Mn5O8, Fe2O3 and Fe3O4 crystals were the dominant structures promoting deNOx reaction on the Fe-Mn2 catalyst. The oxidation of low valence nitrogen oxides by decahedral Mn5O8 on Fe-Mn2 catalyst was an important factor for oxygen resistance. And the various spinel structures over Ni-Mn2, and Cu-Mn2 indicated strong synergistic effects. For the Cu-Mn2 catalyst, the strong synergistic effect of Cu-□-Mn species could promote the dissociation of intermediate -NONO. O2 tended to occupy the surface synergetic oxygen vacancies in Cu-□-Mn species at high temperatures, which could inhibit the dissociation of -NONO and enhance the CO oxidation reaction. The possible reaction mechanisms for CO-SCR over Mn-based catalysts were discussed specifically.