Abstract
NOx storage-reduction (NSR) is a potential approach for the effective removal of NOx under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlOx) with high performance for low temperature NOx storage and release were derived from hydrotalcites precursors prepared by a facile coprecipitation method. The catalysts were characterized by X-ray diffraction (XRD), SEM, N2 adsorption-desorption, H2-TPR, FT-IR, and X-ray photoelectron spectroscopy (XPS) techniques. The Mn-doped MgAlOx catalysts exhibited high NOx storage capacity (NSC) at low temperature range (150–300 °C), which was related to their increased surface area, improved reducibility and higher surface Mn3+ content. The largest NSC measured, 426 μmol/g, was observed for NOx adsorption at 200 °C on Mn15 catalyst (the sample containing 15 wt% of Mn). The in situ DRIFTS spectra of NOx adsorption proved that the Mn-doped hydrotalcite catalysts are preferred for low temperature NOx storage and release due to their ability to store NOx mainly in the form of thermally labile nitrites. NSR cycling tests revealed the NOx removal rate of Mn15 sample can reach above 70% within the wide temperature range of 150–250 °C. Besides, the influence of CO2, soot, H2O and SO2 on NOx storage performance of Mn15 catalyst was also studied. In all, owning to their excellent NOx storage capacity, NSR cycling performance, and resistance to CO2, soot, SO2 and H2O, the Mn-doped MgAlOx NSR catalysts have broad application prospects in NOx control at low temperatures.
Highlights
The Lean-burn engines are gradually being promoted and applied due to their high fuel economy and low pollution emissions
In consideration of excellent NO oxidation activity of Mn-based oxides and potential NOx storage performance of hydrotalcites catalysts, a series of Mn-doped MgAlOx catalysts derived from hydrotalcites were prepared as alternative NOx storage and reduction (NSR) catalysts and their low-temperature performance have been studied in the present work
The chemical composition of the synthesized precursors, the lattice parameters, as well as mean dopant may incorporate into the Mg/Al hydrotalcite structure
Summary
The Lean-burn engines (diesel and lean-burn gasoline engines) are gradually being promoted and applied due to their high fuel economy and low pollution emissions. Guo et al [28] systematically studied the NOx storage and release in the alternative lean-burn/rich-burn atmospheres over Mn2 O3 , Mn3 O4 and MnO2 catalysts at low temperatures (≤ 200 ◦ C) and found that Mn2 O3 showed high NO oxidizability and MnO2 had the biggest NOx storage capacity They suggested that the Mn3+ ions and surface-active oxygen species are the key to high NO oxidation activity. Similar to Pt/BaO/Al2 O3 NSR catalysts, Mg/Al hydrotalcite derived oxides have inferior performance in NOx storage and release at low temperatures. In consideration of excellent NO oxidation activity of Mn-based oxides and potential NOx storage performance of hydrotalcites catalysts, a series of Mn-doped MgAlOx catalysts derived from hydrotalcites were prepared as alternative NSR catalysts and their low-temperature performance have been studied in the present work. It is difficult to differentiate them from the XRD results
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