Cation exchange reaction drives CeMn-montmorillonite catalyst with high dispersion and abundant acidic sites for low-temperature NH3-SCR

Abstract

The development of a cost-effective and eco-friendly catalyst with superior activity for low-temperature selective catalytic reduction of NOX with NH3 (NH3-SCR) is an urgent issue. In this work, a series of CeMn- supported montmorillonite (MMT) were synthesized via a cation exchange reaction. The effects of the valence state of the Mn precursor, acid or base pretreatment of MMT, and the molar ratio of Ce/Mn on zCeMn(x)-MMT(y) were examined. The XRD results revealed that the layer spacing of MMT increased due to Mn3+ of acetate manganese showing the highest cation exchange efficiency. Therefore, Mn(C)-MMT has stronger electronegative and abundant acidic sites, which facilitates the adsorption of NH3. In addition, the dispersion and uniformity of Mn(C)-MMT(12) were improved under the base pretreatment with pH = 12, as confirmed by TEM. To further improve the redox ability, the coexistence of CeO2 favors the production of Mn4+, Ce3+, and adsorbed oxygen species, as confirmed by XPS analysis, thereby facilitating NO oxidation and improving NOX conversion by fast-SCR. Accordingly, 2CeMn(C)-MMT(12) with high dispersion and acidity and abundant Mn species exhibited a NOX conversion of 41% at 100 °C and 85% at 250 °C, invoking an applicable and efficient performance for low-temperature SCR.