The BaFeO(3-x) perovskite catalyst was prepared by sol-gel method for NO(x) storage under lean-burn conditions. During the catalyst precursor calcination, a series of complex solid reactions happened, and the BaCO(3), formed during citric acid combustion, played a key role to react with the spinel species achieving the aimed perovskite. On the Ba-Fe-750F catalyst, the perovskite phase and the small amount of spinel phase were evidenced by XRD, and some well dispersed carbonate was also detected by FT-IR. Under lean-burn conditions, the NO(x) was easily stored on the Ba-Fe-750F catalyst, and its optimized NO(x) storage capacity (NSC), i.e. 333.5 mu mol g(-1), was obtained at 400 degrees C. At above 400 degrees C, the stored nitrate became unstable and decomposed, resulting in the sharp decrease of NSC. Two kinds of the NO(x) storage sites were identified by in situ DRIFTS experiments that the carbonate remaining on the catalyst could transform to monodentate nitrate, and the A site Ba in the perovskite structure could directly bind with NO(x) to form N-bounded nitrate. This BaFeO(3-x) perovskite catalyst was a potential NO(x) storage material with noble metal free. (C) 2010 Elsevier B.V. All rights reserved.