Li-modified MnO2 catalyst and LiMn2O4 for selective catalytic reduction of NO with NH3

Abstract

LiMn2O4 prepared by high temperature solid state reaction, pechini, and citric acid coordination methods was applied in selective catalytic reduction (SCR) of NO with NH3. MnO2 was prepared by high temperature solid state reaction method and the activity was tested as a comparison. The catalysts were characterized by N2 adsorption-desorption, scanning electron microscopy, X-ray diffraction, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, NO temperature-programmed desorption, and X-ray photoelectron spectroscopy. The results showed that high-temperature activities of SCR were improved after the introduction of Li into MnO2. NO conversion on the LiMn2O4 prepared by pechini method was above 90% in the range of 130–260°C; NO conversion on the LiMn2O4 by high temperature solid state reaction method could be kept above 90% in the range of 90–310°C; while the temperature window of MnO2 was only 140–280°C. Compared with MnO2, LiMn2O4 crystal structure not only keeps more manganese cations at a relatively low valence of Mn3+, but also adjusts surface active oxygen. Meanwhile, the existence of Li adjusts surface-acid sites, thus alleviates the unselective oxidation of NH3 in the high temperature, broadens the operating temperature window of NH3-SCR reaction, and improves the tolerance of SO2 of MnO2.