The effect of non-selective oxidation on the Mn2Co1Ox catalysts for NH3-SCR: Positive and non-positive

Abstract

In order to explore the generation of NO2 and N2O on the Mn-Co catalysts in the NH3-SCR process, Mn2Co1Ox (PEG) and Mn2Co1Ox (PA) catalysts, prepared by two different complexing agents, i.e., polyethylene glycol (PEG) and urea as double complexing agents, and ammonia (PA), were further investigated by NO + O2 and NH3 + O2 experiments, besides NH3-SCR test. Catalytic activity and physicochemical properties of the catalysts were compared and analyzed through NH3-TPD, O2-TPD, H2-TPR, XRD, Raman and XPS. The NH3-SCR results show that the Mn2Co1Ox (PEG) exhibits higher NO conversion than Mn2Co1Ox (PA) due to larger amount of lattice oxygen accompanied with more Con+, and surface adsorbed oxygen species, as well as the improvement of surface acidity, proved by O2-TPD, XPS and NH3-TPD, respectively. Furthermore, the separate oxidation experiments show that Mn2Co1Ox (PEG) effectively exhibits the oxidation of NH3 to N2O and also the oxidation of NO to NO2 by O2 respectively, which can influence the catalytic performance. The XRD, XPS and Raman characterization results indicate that Mn2Co1Ox (PEG) contains more Co3O4 than Mn2Co1Ox (PA), that can produce non-selective pure oxidation reaction by the NO + O2 and NH3 + O2 experiments of Co3O4 phase. Information from in situ infrared experiments is that the strongly adsorbed NH3 species on the Mn2Co1Ox (PEG) is susceptible to deep dehydrogenation and react with NOx to produce N2O in the presence of O2. Meanwhile, the oxidation site (Co3O4) can also oxidize NO to more NO2, thereby improving the “fast SCR” reaction. However, if the proportion of oxidation sites is high, NO and NH3 can be oxidized to more N2O will be produced by the reaction between NO and NH3.