Study On Catalysts For The Selective Catalytic Reduction Of NOx Under Lean-burn Conditions

With the development of global automobile industry, the pollution cuased by automobile exhaust has become more and more severe, especially NOX pollution. Therefore people pay more attention to decrease the emission of NOX. The traditional three-way catalyst would be ineffective under lean-burn condition, thus a new type of catalyst for automobile exhaust purification under lean-burn condition is urgently needed to be developed.In this thesis, two kinds of catalysts, perovskite-type-oxide with excellent thermal stability and ZSM-5 molecule sieves have been focused. A series of La-Sr-Co-Fe-O, Ag-LaMnO3 and Cu-Na-ZSM-5 catalysts have been respectively prepared by citrate, wet impregnation and ion-exchanged methods. By combining the catalytic performances and the result of catalysts characterization, the catalysts activities and the reactive mechanism have been investigated.The results showed that perovskite-type-oxide catalyst prepared by citrate method have the excellent catalytic activity and thermal stability. It was indicated that the appropriate amounts of Co and Fe ion not only caused the structure of catalysts close to perfect, but also had a positive effect on the adsorption and the ability of reaction of oxygen.The catalytic activity was obviously improved by loading metal Ag ion dued to highly dispersed metal Ag ion, which favors the adsorption-activation of NO and O2 on the catalysts surface and induce some Schotty defects in the form of anionic vacancies and high valence ion. Pretreatment in H2 increased the conversion of NO and propene by inducing oxygen vacancy, which would be favorable for the transportation of lattice oxygen species.Cu-Na-ZSM-5 molecule sieves prepared by ion-exchanged method have excellent activity and the skeleton of molecule sieves aren't destroyed after aged reaction process. The Bronsted acid sites play a positive influence in the reaction, but not absolutely necessary and disappears partly in the aged reaction, which caused to decrease the catalytic activity.