Study On The Supported Nsr Catalysts With The Noble Metal Pt Totally Replaced By Perovskite

In traditional NSR catalysts noble metals are often used as the oxidative and reductive component. However, the resources of noble metals are very limited, and their prices are also very high. So, replacement of noble metals by base oxides is very necessary. Improved properties of mixed oxides against simple ones are well known, especially in the environmental protection field. Among the mixed oxides perovskites play an important role for fundamental studies, because their low cost, high thermal and mechanical stability, great diversity, and excellent redox property. However, their applicability was limited because of their lower surface area and increased tendency to sinter. One of the solutions to solve the problem is to disperse them on a support with large surface area and high thermal stablity. In order to avoid the reaction of precursor salt with the support to form other stable compounds, an in situ preparation method was used to support the perovskite La_1-xSrxCoO3 on the support ZrTiO₄.The support ZrTiO₄ was prepared by co-precipitation method. Supported LaCoO3 perovskite with 20 wt% loading was obtained by wet impregnation of support ZrTiO₄ with a solution of La and Co nitrates, and citric acid. XRD and EXAFS techniques were used to characterize the structure of the perovskite in La_1-xSrxCoO3/K/ZrTiO₄, which shows that the sample LaCoO3/K/ZrTiO₄ possesses more crystallized perovskite phase than other catalysts. Its BET surface area is much larger than the bulk perovskite and other supported perovskites, making the perovskite phase possess higher dispersion and smaller crystallite size.The perovskite catalysts show more excellent activities for NO conversion and NOx storage than the noble metal Pt-based catalysts. On one hand, there are much more oxygen vacancies in the perovskite LaCoO3, facilitating the adsorption and oxidation of NO; on the other hand, the loading of perovskite is much larger than that of Pt, increasing the contact efficiency between perovskite and storage component K, which is favorable to NOx storage. The results of in-situ DRIFTS indicate that in the perovskte catalysts nitrogen oxides are mainly stored via the"nitrite route". H2-TPR and SEM results show that perovskite catalysts are sensitive to SO2. High concentration of SO2 can react not only with the K sites but also with the perovskite to form sulfates, resulting in the destruction of perovskite structure and a significant agglomeration of elementary particles. In order to improve the NOx storage performance of supported perovskite NSR catalysts, the Ce_1-xZr_xO₂ (x=0⁰.3) solid solution was prepared and used as supports. XRD patterns and XPS measurements evidenced the formation of a pure perovskite phase, preferentially accumulated on the outer surface. The perovskite catalyst LaCoO₃/K₂CO₃/Ce_0.8Zr_0.2O₂ shows better storage performance than ZrTiO4 supported catalysts, which is related to the strong oxygen storage ability of Ce0.8Zr0.2O2. This catalyst also shows better sulfur tolerance than other supported catalysts.