NSR Performances And Kinetic Study For NO Oxidation Over Perovskite-type La_1-xSr_xCo_0.8Fe_0.2O₃ Catalysts

The La_1-xSr_xCo_0.8Fe_0.2O₃?x=0, 0.3, 0.4, 0.5, 0.6? perovskite catalysts were prepared according to complexation method in which citric acid and EDTA were used as complexing agent. The obtained perovskite catalysts were applied in NO_x storage and reduction experiment to evaluate catalytic activity. The structures of perovskite catalysts with different Sr doped amounts were investigated by a series of characterizations such as XANES and H₂-TPR. The catalyst with the suitable substitute proportion?x=0.5? had the maximum lattice defect, which resulted in a large amount of oxygen vacancies and high valence Co4+, all of these would lead to that the La0.5Sr0.5Co0.8Fe0.2O3 possessed a stronger oxidizing ability and more active sites. Increasing the Sr substituted proportion, Sr could not dope into the perovskite crystal lattice totally, and a certain amount of impurity phase was formed, such as SrCoO₂.5+?, which will lead to decrease the amount of oxygen vacancies. After the NO-to-NO₂ oxidation and NO_x storage capacity?NSC? tests on the catalysts, it was found that the La0.5Sr0.5Co0.8Fe0.2O3 sample performed the strongest oxidation ability and the highest NSC, it was indicated that the catalyst structure had an import impact on the catalytic performance.The effect of reaction temperature and space velocity was studied. Compared with LaCo0.8Fe0.2O3, the catalysts with Sr doping could improve the NSR activity greatly, especially under high space velocity condition, on the other hand, the temperature range of NO_x complete conversion became wider, and the catalyst La0.5Sr0.5Co0.8Fe0.2O3 showed the prime catalytic performance on account of that the catalyst more oxygen vacancies were existed which led to better oxidation reaction.The reaction kinetics of NO-to-NO₂ were also surveyed. Reaction temperature and gas concentration were the most important factors in kinetic research, hence the relationship between the two factors and NO oxidation rate over the catalysts La_1-xSr_xCo_0.8Fe_0.2O₃ were investigated, reaction activation energy and reaction order could be obtained. The results indicated that the reaction pathway of NO oxidation had no significant change after Sr doping and the various conversion was ascribed to that the amount of activity site was different. The reaction rate equation is r = kf [NO]0.40[O₂]0.45, and the reaction mechanism over the Sr doped catalysts was speculated and two kinds of reaction pathway possibly existed. It was also pointed out that surface defect sites played an import role in the oxidation process.