The High-Temperature Performance of Pt/Ba/Co_xMg_1-xAl₂O₄ Catalysts for Lean-Burn NO_x Removal

A series of catalysts Pt/Ba/Co_xMg_1-xAl₂O₄ supported by cobalt doped hydrotalcite materials were prepared by coprecipitation-impregnation method for NO_x removal at 250–500 °C. The techniques of XRD, TEM, XPS, BET, H₂-TPR, NO_x-TPD, and FT-IR were employed to study the structure and properties of the catalysts. After Co doping, the specific surface area of the catalyst is significantly increased, while the number of surface reactive oxygen species is increased, making NO more easily oxidized to NO₂, which is conducive to NO_x storage. Meanwhile, XRD and TEM results show that Co doping also promotes the dispersion of BaCO₃, which is the NO_x storage site. In addition, the results of TEM and XPS before and after high temperature reaction showed that the active center Pt maintained good dispersion, no obvious sintering occurred, and the valence state of Co remained unchanged. The above characterization results show that the addition of Co significantly improves the storage capacity and thermal stability of the storage intermediates in the catalyst, that is, enhances the elimination performance of lean burn NO_x at high temperatures. Co-doped catalysts Pt/Ba/Co_xMg_1-xAl₂O₄ (x = 0.1, 0.3 and 0.5) showed better high-temperature activity than Pt/Ba/MgAl₂O₄. Pt/Ba/Co_0.3Mg_0.7Al₂O₄ showed the highest De-NO_x efficiency of 93.2% at 400 ºC and 88.7% at 450 ºC, respectively.