Effect of iron doping on SO2 and H2O resistance of honeycomb cordierite-based Mn–Ce/Al2O3 catalyst for NO removal at low temperature

Abstract

Honeycomb cordierite-based Mn–Ce/Al2O3 (Mn–Ce/Al2O3–C) and Fe–Mn–Ce/Al2O3 (Fe–Mn–Ce/Al2O3–C) catalysts were prepared by an impregnation method and investigated in low-temperature selective catalytic reduction (SCR) of NO with NH3 at 100 °C. The Fe–Mn–Ce/Al2O3–C catalyst exhibited not only higher catalytic activity, but also much better SO2 and H2O resistance in the presence of 30 ppm SO2 and/or 5 vol% H2O than Mn–Ce/Al2O3–C. After doping Fe, the NO conversion of Mn–Ce/Al2O3–C catalyst displayed an increasing trend from 79 to 84% in the absence of SO2 and H2O at 100 °C under a gas hour space velocity of 1667 h−1. The results of characterization indicated that addition of Fe was advantageous to increase BET surface area, pore volume and inhibit loss of surface Mn and Ce species. Additionally, it was helpful for generating higher concentration of Mn4+, more chemisorbed oxygen and more uniform dispersion of amorphous Mn and Ce in the surface of catalyst, which were beneficial to interact with reactants. Furthermore, in contrast to Mn–Ce/Al2O3–C, the SCR activity of Fe–Mn–Ce/Al2O3–C catalyst in the presence of H2O, SO2 and H2O and SO2 were 79, 75 and 64%, with the increase of 14, 18 and 19%, respectively. It is indicated that the addition of Fe could inhibit sulfate formation and thus enhance SO2 resistance. XPS results reveal that the doping of Fe into the ceria lattice led to some Ce4+ transferred into Ce3+ in order to maintain the electrical neutrality, thereby facilitating the reduction of Ce4+ → Ce3+ and the formation of oxygen vacancies. NH3 temperature-programmed desorption (TPD) results imply that the doping of Fe onto Mn–Ce/Al2O3–C can remarkably improve the distribution and concentration of acid sites. All the above factors contributed to the improvement of overall NH3 SCR performance of the Fe–Mn–Ce/Al2O3–C catalyst compared with that of the Mn–Ce/Al2O3–C catalyst.