Enhanced low-temperature activity and huimid-SO2 resistance of MnFe-based multi-oxide catalysts for the marine NH3-SCR reaction

Abstract

Several MnFe-based multi-metal oxides were synthesized as NH3-SCR catalysts by a simple coprecipitation method for abating NOx of marine diesel exhausts. The Co and Nb-doped MnFeCeAl catalysts exhibit NOx conversion over 90% and N2 selectivity above 95% at 180–270 °C, especially the MnFeCeAlCo catalysts can inhibit nearly all sulfate species growth within 150 ppm humid-SO2 gases at 225 °C. The structural characterization results revealed that Co, Nb, Sm, and Sb doping can enhance interactions among different components and promote active component dispersion. Temperature programmed analysis indicated that the Co doping is not only more favorable for improving redox properties, but can also enhance the surface acidity, which are advantageous to improve the activity, N2 selectivity, and humid-SO2 resistance. Moreover, the XPS results implied that the binding energy shift or the valence variation of the Sm, Sb, Nb, and Co species on catalyst surfaces are favored to raise the atomic ratios of high-valent Mn species and surface adsorbed oxygen, which can promote the redox property significantly and further facilitate SCR activity. Accordingly, the excellent activity and humid-SO2 tolerance of the MnFeCeAlCo catalyst should attribute to its lower redox temperature, strong interaction between oxides, 47.3% surface Mn4+/Mn3+ species, and 71.8% adsorbed oxygen, which provide a method for improving the SCR performances of MnFe-based catalysts with humid SO2 resistance.