Novel manganese-based assembled nanocatalyst with “nitrous oxide filter” for efficient NH3-SCR in wide low-temperature window: Optimization, design and mechanism

Abstract

It is still a challenge for de-NOx catalysts to have high activity and N2 selectivity in a wide low-temperature operating temperature window. In this work, we used layered zeolite-like montmorillonite as the support and then obtained a composite catalyst with satisfactory NOx conversion and excellent N2 selectivity in the temperature range of 100–300 °C with the method of pillaring modification, active component doping, and catalyst assembly. It has been proved that doping rare earth elements can improve the redox ability of the catalyst, and WO3 modification can enhance the acidity of the catalyst. The redox ability and the surface acidity of the catalyst system were balanced by assembling the WO3-modified catalyst and the WO3-unmodified catalyst. Besides, we found the composite Pr1Mn9/Fe7Ti3-Wu-mmt catalyst had the best catalytic activity and N2 selectivity only when the reaction gas first passed through the catalyst modified by WO3, in which the WO3-modified catalyst acted as the role of nitrous oxide filter. What’s more, according to the results of in situ DRIFTS, it can be indicated that the montmorillonite-supported catalysts in this work followed the L-H mechanism and E-R mechanism; while the E-R mechanism was dominant when the catalyst was modified by WO3. The results in present work indicate that the novel strategy of assembling catalysts is practicable to obtain an efficient de-NOx catalyst with a wide low-temperature operating temperature window, high NOx conversion, and high N2 selectivity. Furthermore, the novel assembly strategy of tandem catalysis with stronger acidity sites and redox sites in turn “acidityu & redoxd” can be extended to other SCR catalytic systems.