The NSR Performance Of The Ba-based Perovskite-type Catalysts

A series of Ba_1-xMg_xFeO₃, Ba_1-xCa_xFeO₃and Ba_1-xSr_xFeO₃（x=0,0.1,0.2） wasprepared by a sol-gel method to remove NO_xexhausted from lean-burn diesels. Wefound that the Ba_0.8Mg_0.2FeO₃perovskite sample possessed the best NO_xstoragecapacity （NSC） amoung these catalysts. The NO_xstorage reduction （NSR）experiments were tested at200⁴00℃. These results show that the NO_xeliminationefficiency of the Ba00.8Mg0.2FeO₃sample was slightly worse than that of the BaFeO₃sample although the former has a bigger NSC. The optimal temperature of the NSRperformance for BaFeO₃perovskite is350℃with NO_xeliminated efficiency morethan90%.To broaden the working temperature window of the BaFeO₃perovskite, a seriesof BaFe_1-xPd_xO₃（x=0.01,0.02,0.03） perovskite-type catalysts was prepared with thesame sol-gel method. The XRD patterns of the catalysts show that the intensity of thediffraction peaks becomes stronger after Pd doping. And, the intensity of thediffraction peaks of the BaCO₃and BaFe₂O₄phases decreased or even disappearedfollowing the increasment of Pd doping amount. It indicates that Pd was doped intothe perovskite crystal lattice perfectly. The NSR results show that theBaFe_0.98Pd_0.02O₃sample has the best catalytic activity for De-NO_xunder thealternative lean-burn/fuel-rich atmospheres. The NO_xconversion reached87%afterusing H2as reducing agent instead of C3H6at the temperature range of350⁴00℃.Moreover, we also found that after pre-reduction by H₂the NO_xconversion of theBaFe0.98Pd0.02O3perovskite increased to90%at the temperature range of250⁴00℃.Moreover, the variation of the produced CO₂illustrates that the BaCO₃dispersed onthe surface of perovskite participates in the NO xstorage-reduction process at250⁴00℃.Furthermore, we also investigated the NSR performance of the coupledBaFeO₃+Cu-ZSM-5catalysts to suppress the usage of the noble metals for theaftertreatment systems of the diesel engines. Comparing with the impregnationmethod, the combined Cu-ZSM-5zeolite catalyst prepared by the ion exchangemethod could improve the De-NO_xactivity of BaFeO₃significantly, and the NO_x conversion at300³50℃mantaining at about90%. FT-IR results show nitrate speciesappeared after NSR reaction in the Cu-ZSM-5sample prepared by ion exchangemethod. It indicates that Cu-ZSM-5sample may not only reduce NO_xto N2but alsostore NO_x.