A series of lean-burn NO trap (LNT) catalysts Pt/K/Al2O3-TiO2-ZrO2 were prepared by sequential impregnation By altering support calcination temperature and K loading the distribution state of the storage medium K on different catalysts is carefully investigated Pyridine-IR results show that a lot of hydroxyl groups exist on the supports calcined at low temperatures (<800 degrees C) which can react with the supported K2CO3 possibly forming -OK groups The in situ DRIFTS results indicate that the dominant NOx storage species are monodentate or/and bidentate nitrates As the calcination temperature is increased to 800 C or higher much less hydroxyl groups are detected on the surface of Al2O3-TiO2-ZrO2 In this case most potassium exists in the form of K2CO3 on Al2O3-TiO2-ZrO2 which can transform to free ionic nitrates during NOx storage High K loading and high calcination temperature facilitate the formation of K2CO3 which possesses higher NOx storage efficiency but lower sulfur resisting and regeneration ability than -OK groups (c) 2010 Elsevier B V All rights reserved