Modification of Mn-Fe mixed oxide catalysts for low-temperature NH3-SCR of NO from marine diesel exhausts

A series of Mn-Fe mixed oxides doped with CeO2, Al2O3 and Sm(2)O(3 )were prepared by a simple coprecipitation method and applied as NH3-SCR catalysts to treat the NO of marine diesel exhausts. The effects of these promoters on the structural properties of Mn-Fe oxides were investigated by XRD, BET, SEM, FT-IR, TG, TPR, TPD and XPS techniques. The results of catalytic tests showed that the Mn-Fe oxide catalyst co-doped with CeO2, Al2O3 and Sm2O3 exhibited the best deNOx activity and SO2 tolerance. The XRD, BET and SEM results revealed that the addition of Ce promoted the formation of Mn-Fe solid solutions and the introduction of Al enhanced the dispersion of different elements in the catalysts. The H2-TPR and NH3-TPD results suggested that the reduction properties were adjusted to a good balance and the surface acidity sites greatly increased by the addition of Ce, Al, and Sm species, which were in agreement with the improvement of the catalytic activity below 240 celcius. In addition, the XPS spectra indicated that the high concentrations of Fe3+and Mn3+ in surfaces of catalysts modified with Al and Sm could significantly enhance the redox catalytic cycles owing to the electronic transfer between them, and the Sm doping could simultaneously raise the fraction of Ce3+ by the reduction of Mn(4+ )and Ce4+ and thus suppress SO2 poisoning owing to the electron transfer between M4+ and SO2, which were contributed to the improvement of activity and SO2 resistance of mixed oxide catalysts.