A Study On The No_x Storage-Reduction Catalysts Of The BaCo_1-xFe_xO₃ Perovskite And The Supported Ba/Co/TiO₂-ZrO₂

A series of NSR catalysts including bulk perovskite BaCo1-xFexO₃-δ(x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0) and supported Ba/Co/ZrTiO4 were prepared. Their structures, properties and NOx storage mechanism were characterized by the techniques of XRD, BET, in-situ DRIFTS, FT-IR and H₂-TPR.Calcination condition shows obvious effect on the BaCoO₃-δperovskite. In flow air which is pretreated by soda lime to removed CO₂, the perovskite is more completely formed. The NOx storage capacity (NSC) and oxidation ability of the sample calcined at 700 oC are better than other samples. However, it exhibits poor sulfur resistance and small surface area.The support ZrTiO4 was prepared by co-precipitation. Ba and Co nitrates were supported on ZrTiO4-700 support by wet impregnation. After calcination, new active phase BaTiO₃ and BaTi0.75Zr0.25O₃ are formed. Compared with bulk perovskite, a much higher specific surface area of 20 m2/g is obtained, as a result, more active sites can be accessed on the supported sample, improving the oxidation ability of the catalysts and facilitating the diffusion of the NO₂. Although BCTZ-700 catalyst shows better NOx storage capacity and sulfur resistance than bulk perovskite, the active phases on the support can also easily react with SO₂ during the sulfate process, in addition, the storage component can be reduced to Ba and Co oxides during reduction regeneration, resulting in the total destruction of perovskite structure. In comparison, BCTZ-600 catalyst possesses higher NSC, better sulfur resistance and reduction performance. The active phases on the support are better dispersed, whose structure is only destroyed partly during the sulfur-aged process. After reduction regeneration, the NOx storage capability of sulfur-aged sample is almost the same as that for the fresh sample. In-situ DRIFTS results show that the main NOx storage species are the ionic nitrate and bidentate nitrate on the supported catalysts.To enhance the sulfur resistance of the catalysts, a series of BaCo1-x FexO₃ catalysts were prepared using the same preparation method. After sulfur-aging, the NSC of Fe-doped BaCo0.8 Fe0.2O₃ only decreases 3%, suggesting that the sample possesses rather good sulfur resistance performance. However, its NSC is only 31% of that for the non-doped catalyst BaCoO₂.93. As the content of doped Fe is increased to 40%, the formed BaCo0.6 Fe0.4O₃ exhibits higher NOx storage capacity and better sulfur resistance. The NSC of the fresh BaCo0.6 Fe0.4O₃ is nearly the same as that for the fresh BaCoO₂. 93. After sulfation it decreases ¹8%. The results of FT-IR show that the main stored species are bulk nitrate and monodentate nitrate. The main redox active sites are Co sites.