Enhanced activity of CuO/K2CO3/MgAl2O4 catalyst for lean NOx storage and reduction at high temperatures

Herein, we designed a new NOx storage and reduction CuO/K2CO3/MgAl2O4 catalyst operating within the high temperature region of 350–550 °C. Compared with the Al2O3 supported catalyst with the same Cu and K loading, it exhibits superior NOx storage and reduction performance. The NOx reduction percentage (NRP) of the CuO/K2CO3/MgAl2O4 catalyst remains above 90% over a wide temperature range (400–550 °C), and reaches the highest NRP of 99.9% at 450 °C with the N2 selectivity of 99.7%. Uncovered CuO particles with better reducibility exist on the CuO/K2CO3/MgAl2O4 catalyst, with the high NOx oxidation and reduction ability above 400 °C. Potassium carbonates on the CuO/K2CO3/MgAl2O4 catalyst mainly exist in three forms, including free ionic carbonate, bridging bidentate carbonate and chelating bidentate carbonate. Under lean-burn conditions, most of carbonates on the CuO/K2CO3/MgAl2O4 catalyst can store NOx to form nitrates, but only parts of them participate in NOx storage on the CuO/K2CO3/Al2O3 catalyst. The MgAl2O4 support offers additional sites for NOx adsorption, while the formed nitrate on it shows low thermal stability. So, NOx is mainly stored on K2CO3 at high temperatures, because MgAl2O4 can enhance the thermal stability of the supported K2CO3 on it. Our results show that the thermal stability of K2CO3 directly determines the thermal stability of the formed nitrates. Accordingly, the CuO/K2CO3/MgAl2O4 catalyst shows the high NSR activity because of the efficient redox ability of CuO and high thermal stability of K2CO3 at high operating temperatures.