Catalytic Soot Combustion And NO_x Storage Reduction On Pd-K-MgAlO Composite Oxides

With the development of modern society, the application of vehicles is becoming moreand more popular and the amount of vehicles is also increasing. The exhaust emissions fromvehicles contain harmful substances such as soot particulates and nitrogen oxides （NO_x）,which can bring about great harm to the environment and human health. With the increasinglystringent emissions regulations, the removal of soot particulates and NO_xhas attracted moreand more attention, but only Internal purification technologies can not fulfill the demands. Sofar, efficient catalysts are significantly needed for after-treatment technology.In this study, a series of Pd-K-MgAlO catalysts were prepared by coprecipitation andimpregnation method with hydrotalcites derived MgAlO oxides as supports. The catalystswere characterized by BET, XRD, HRTEM; the catalystic activities for soot combustion andNO_xstorage-reduction （NSR） activity were evaluated by temperature programmed techniques.The results showed that MgAlO support possessed a high specific surface area of96.5m²/g. Itwas found that Mg-Al hydrotalcite phase was successfully obtained in the precursors. Aftercalcinated at950℃, MgO and MgAl₂O₄crystalline phase appeared in the MgAlO support.For the Pd and K containing catalysts, we can not find the potassium crystalline phase becauseK is highly dispersed on the catalysts, while PdO crystalline phase appeared in the catalysts.HRTEM characterization revealed that the noble metal palladium was highly dispersedon the catalysts, and this is in accordance with the results of XRD. The dispersion on thecatalysts（Pd-MgAlO-400, Pd-MgAlO-850, Pd-K-MgAlO-400-850and Pd-K-MgAlO-850-850） is23.3%,22.2%,10.2%and7.2%, respectively.The catalytic activities tests showed that the presence of NO₂in the reactant gas candecrease the soot ignition temperature to320℃on Pd-MgAlO, which is lower than that inthe presence of O₂in the reactant gas （450℃）; The pre-stored NO_xon Pd-MgAlO catalyst candecrease the soot combustion temperature to290℃. This suggested that the gas NO₂couldplay an important role in the catalytic combustion of soot. The catalysts Pd-K-MgAlO-400-850and Pd-K-MgAlO-400-850showed much high catalytic activity of NO_xstorage and reduction.The reduction temperature was decreased to about200℃. The stored NO_xin the catalystswas wholly removed in the redox reaction by CO.