The low-temperature selective catalytic reduction (SCR) of NOx is a promising technology for removing NOx from flue gases. However, the vulnerability of Mn-based catalysts to SO2 and H2O poisoning makes them unsuitable for industrial application. Herein, catalysts based on the MnOx/SAPO-34 catalysts were prepared by conventional impregnation and an improved molecularly designed dispersion method for use in the low-temperature SCR. The improved molecularly designed catalyst containing 20 wt% of MnOx exhibited high low-temperature NH3-SCR activity. Nearly 90% of the NOx was converted exclusively to N2 at 160°C using this catalyst. The structure and morphological analyses of the catalyst showed that the amorphous MnOx was well dispersed on the surface of the support. The reasons for the high performance of the catalysts were ascertained using surface N2 adsorption, XPS, H2-TPR and NH3-TPD. The results of these analyses indicated that high specific surface area and the redox capability, of the abundant Mn4+ and Mn3+ species, coupled with the surface chemisorbed oxygen and strong acid sites had a significant effect on the SCR reaction. In addition, the effects of SO2 and H2O on activity of the catalysts were also investigated and it was found that the highly dispersed 20 wt% MnOx/SAPO-34 catalyst exhibited better SO2 poisoning resistance than the other impregnated catalysts.
Keywords: Highly dispersed; MnOx/SAPO-34 catalyst; NOx; low-temperature NH3-SCR; molecularly designed dispersion method.