Multifunctional hydrotalcite-derived K/MnMgAlO catalysts used for soot combustion, NOx storage and simultaneous soot–NOx removal

Abstract

A series of hydrotalcite-derived K/MnMgAlO catalysts were synthesized by co-precipitation and impregnation methods. Their catalytic performances for soot combustion, NOx storage and simultaneous soot–NOx removal were evaluated, respectively. Techniques of TG/DTA, BET, XRD, EXAFS, and in situ DRIFTS were employed for catalyst characterization. The catalyst K/Mn1.5Mg1.5AlO containing 7.5wt% K shows not only the highest soot oxidation rate of 58.0μgs−1 per gram catalyst, but also the maximal NOx reduction percentage of 26.9%. Over the catalysts containing K less than 10wt%, the soot combustion follows oxygen spillover mechanism, while over those containing more than 10wt% K it follows a different mechanism involving the participation of potassium nitrate species. In situ DRIFTS results indicate that introduction of proper amount of K can facilitate the formation of monodentate nitrate, which shows higher reactivity with soot than nitrite, chelating bidentate nitrate and ionic nitrate species. In the catalysts promoted by K, a new phase namely K2Mn4O8 was identified, which is highly active for soot combustion and NOx reduction by soot.