Study on the Ce-Zr-Based Pd Catalysts Modified by Rare Earth Pr Used for the Purification of Automobile Exhaust

Study on the Ce-Zr-Based Pd Catalysts Modified by Rare Earth Pr Used for the Purification of Automobile Exhaust
　　1. A series of industrialγ-Al2O3 were modified by La2O3, they were characterized by using XRD technique. The results reveal that all samples calcined at 950℃have the same structure with freshγ-Al2O3, and the sample modified by wetness impregnation shows the lowest intensity of the diffraction peaks.2. A series of PrxCe0.65-xZr0.35O2(xPCZ) complex oxides with various atomic ratios were synthesized by the citric acid complexation method, and characterized by using TG/DTA、XRD、XPS and H2-TPR techniques. The results of TG/DTA reveal that Ball Neodymium Magnets all the samples have the same weight-loss stages. With the increase of the dopant praseodymium, the formation of complex oxides becomes more difficult. The XRD results display that all samples calcined at both 500℃and 850℃show the same cubic phase structure with the pure CeO2 oxide, while with the increase of the dopant praseodymium, the diffraction peaks shift to higher angle to some extent, Compared with the samples calcined at 500℃, all peaks of the samples calcined at 850℃are more intense and narrow obviously.
　　The XPS results show that Pr and Ce atoms on the surface of all the samples present +4 chemical state, meanwhile, compared with the samples calcined at 500℃, Pr and Ce atoms of the samples calcined at 850℃can transfer from bulk to surface, furthermore, Pr atoms transfer more easily than Ce. The H2-TPR results also reveal that all the samples calcined at 500℃have only a reduction peak. When the percent of the dopant praseodymium increases, the temperature of reduction peak increases, but the peak area seems unchanged. For the samples calcined at 850℃, there are two reduction peaks in the H2-TPR curves. As the amount of praseodymium increases, the low-temperature reduction peak shifts to lower temperature direction, and the high-temperature reduction peak shifts to higher temperature direction, but the total area of these peaks keeps unchanged. The samples without Ce always present reduction peaks at the highest temperature and give the smallest peak area.3. A series of noble metal Pd-based catalysts were prepared by wetness impregnation method, the precious metal http://www.chinamagnets.biz/ was loaded to mixed powder using impregnation directly.
　　The three-way and propane combustion performance of these catalysts were evaluated by using CO、NO and C3H8 as the reactants. The results reveal that CO、NO and C3H8 cannot be eliminated at the same time or at the same temperature region. The propane combustion results show that the C3H8 oxidation efficiency is in good accordance with the reduction tendency of the complex oxides.4. Another series of noble metal Pd-based catalysts were prepared by the citric acid complexation and wetness impregnation method step by step. The catalysts were characterized by using H2-TPR technique. The results reveal that with the increase of the dopant praseodymium there is no obvious difference in the reduction property among these catalysts. The samples without Ce show the worst reduction property.