Effect of the calcination conditions on the NOx storage behavior of the perovskite BaFeO3−x catalysts

The BaFeO3−x perovskite catalyst was prepared by sol–gel method for NOx storage under lean-burn conditions. During the catalyst precursor calcination, a series of complex solid reactions happened, and the BaCO3, 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 NOx was easily stored on the Ba–Fe–750F catalyst, and its optimized NOx storage capacity (NSC), i.e. 333.5 μmol g−1, was obtained at 400 °C. At above 400 °C, the stored nitrate became unstable and decomposed, resulting in the sharp decrease of NSC. Two kinds of the NOx 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 NOx to form N-bounded nitrate. This BaFeO3−x perovskite catalyst was a potential NOx storage material with noble metal free.