A novel highly active and sulfur resistant catalyst from Mn-Fe-Al layered double hydroxide for low temperature NH3-SCR

For low temperature selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR), MnOx-based catalysts are very promising, but suffer from severe sulfur poisoning. In this contribution, we report a novel catalyst Mn1Fe0.25Al0.75Ox synthesized by calcination of Mn1Fe0.25Al0.75-NO3 layered double hydroxide (LDH) precursor. We demonstrated the LDHs derived mixed-oxide catalysts (MnAlOx and MnFeAlOx) possess much better performance than the conventional doped catalyst Mn-Fe/gamma-Al2O3 in a wide low temperature range (80-250 degrees C). At 150 degrees C, the NOx conversion of Mn1Al1Ox and Mn1Fe0.25Al0.75Ox reached 97.6% and 96.3%, respectively, higher than that of Mn-Fe/gamma-Al2O3 (88.1%). We also revealed that the addition of Fe can significantly increase the sulfur resistance of MnAlOx catalysts. In the presence of 100 ppm SO2, the NOx conversion of Mn1Fe0.25Al0.75Ox maintained as high as 76.6% even after 12 h, which is much higher than that of Mn-Fe/gamma-Al2O3 (15.8%). Mechanism studies suggested that the addition of Fe can increase the surface acidity, the mobility of surface oxygen, and the amount of surface adsorbed oxygen (O-beta). In-situ FTIR analyses demonstrated that the addition of Fe can significantly decrease the formation rate of SO42- and thus inhibit the sulfur poisoning of catalysts.