Preparation And Evaluation Of Mg₃Mn_xAl_1-xand Co_xMg_3-xAl Ternary Layered Double Hydroxides Derived NO_x Storage And Reduction Catalysts

The emission of NOx will cause multiple hazards to the atmospheric environment and human health,and its control methods have attracted wide attention.Because NOx can not be effectively reduced by traditional three way catalyst under lean bum conditions,NOx storage/reduction technology arises at the historic moment.In this paper,the preparation and properties of new NSR catalysts were studied by using CoxMg3-xAl-CO3 and Mg3MnxAl1-x-CO3 hydrotalcite derived oxides as carriers.In this paper,Mg3MnxA1-xCO3 AMO-LDH and CoxMg3-xAl-CO3 AMO-LDH hydrotalcite was successfully synthesized by coprecipitation method,and the Pt and BaO modification of ternary hydrotalcite derived oxide was carried out.A variety of technical means were used to systematically characterize the materials,and the NO oxidation properties,NOx storage properties and NOx storage/reactivation properties of the catalysts were studied.In addition,the reaction mechanism is briefly analyzed.The experimental results show that for Mg3MnxAl1-xCO3 type hydrotalcite derived NSR catalysts,Mn3+greatly substituted for Al3+to change the microstructure of the samples.At 250?,Mg3Mn0.5Al0.5Ox has the best NOx storage capacity(0.52 mmol/g).The NOx storage capacity of the catalyst increased from 0.52 mmol/g to 0.61 mmol/g with lwt%Pt loading.In addition,the NOx storage/reduction performance of the material was tested.After 9 lean-rich cycles,the removal rate of NOx was only 68%,indicating that the reduction and stability of the catalyst IPt/Mg3Mn0.5Al0.5Ox still need to be strengthened.It is found that the presence of CO2 strongly inhibits the NOx storage performance of the catalyst,indicating that CO2 and NOx have strong competitive adsorption.For CoxMg3-xAl-CO3 hydrotalcite derived NSR catalysts,the best loading ratios of Pt and BaO are 1wt%and 20wt%respectively.The best NOx storage capacity of IPt/20Ba/Co1Mg2AllOx catalyst appears at 300?(1.38 mmol/g),and the adsorption rate of NSC and NOx increases with the adsorption temperature increasing.The NOx storage reduction performance of the material was tested.The results showed that the catalyst still maintained excellent performance after 9 cycles,and the removal rate of NOx could reach 82.2%.The study found that CO2 and NOx had strong competitive adsorption,and the storage capacity of NOx dropped from 1.38 mmol/g to 1.19 mmol/g(6%CO:).In addition,the presence of water vapor has an effect on the performance of the catalyst 1IPt/20Ba/Co1MgZAlOx,so that the storage capacity of NOx decreases from 1.38 mmol/g to 1.01 mmol/g(5%H2O).Two kinds of hydrotalcite derived oxides play an important role in the NSR process as carrier and storage component,so that the storage performance of NOx and the storage/reduction performance of NOx have been greatly improved.