Effect of Copper Doping on Lean NOx Trap Performance of Pt/Ba/CuxMg1-xAl2O4 Catalysts at High Temperatures

A series of Pt/Ba/CuxMg1-xAl2O4 catalysts with Cu doping was synthesized and used in high-temperature NOx storage reduction reaction. The results demonstrate that BaCO3, the NOx storage component, redisperses in the NOx storage reduction process. Moreover, the De-NOx activity of the catalysts at high temperatures was determined by the NOx storage capacity, rather than the NO oxidation and NOx reduction ability of the catalysts. The NOx storage capacity of the catalysts is directly linked to the thermal stability of nitrate species stored on the catalysts. NOx mainly exists in the form of ionic nitrate species on Pt/Ba/MgAl2O4, while NOx mainly co-exists as ionic nitrate and monodentate nitrate species on the Cu-doped catalysts. We discovered that monodentate nitrate species show higher thermal stability than ionic nitrate species. As a result, the Cu-doped catalysts exhibit the larger NOx storage capacity and hence the higher De-NOx activity. At the temperature range from 450 degrees C to 500 degrees C, the addition of Cu greatly enhanced the NOx removal percentage of the catalysts. Among all the catalysts, Pt/Ba/Cu-0.1Mg0.9Al2O4 has the highest De-NOx activity with NOx removal percentage about 90% at 450 degrees C.