Study On Automobile Exhaust Purification Catalyst

With the development of automotive industry, vehicle exhaust emissions on the environment caused severe damage effect. How to reduce harmful emissions from vehicle exhaust has become the focus problem. Although the automotive catalytic technology has mature, whose core technology is monopolized by developed countries and still in a confidential stage, the automotive catalysts of our country mainly rely on import at present. Therefore, the research on the automotive catalyst and the preparation with the international advanced level performance are partiicuilarly important for the national economy. This paper has prepared the oxygen storage material of three-way catalyst in gasoline engines and PM purification catalyst in diesel engines, and investigated the preparation condition and elements doping on the properties of the catalysts. Meanwhile, the relationship between structure and properties were discussed.Some specific conclusions are drawn from this work as follows:1. Peroskite-type catalyst modified by K in A site obtains better catalytic activity, and La0.8K0.2CoO3 has the best catalytic activity, which has two reasons that cause its good catalytic activity:(1) K doping can change the structure of perovskite, and increase oxygen vacancies in the perovskite; (2) The valence of K+ in the compound is lower than that of La3+, leading to some Co3+ turn intoCo4+, while the oxidability of Co4+ is stronger than Co3+.2. The doping modification of B site can also improve the catalytic activity of perovskite-type catalysts, while the doping in B site can increase the limit of A site doping. The possible cause is that the ionic radius of Fe2+ and Pd2+ is larger than Co3+, Increasing the dosage of K can maintain the stability of perovskite structure, resulting in the formation of more oxygen vacancies in perovskite-type catalysts, thereby enhancing the catalytic activity.3.The best calcining temperature and calcining time of La0.8K0.2CoO3 are 800℃and 4h, respectively.4. In the CeO2-ZrO2 oxygen storage material, the addition of ZrO2 can improve the oxygen storage capacity and high temperature resistance performance of oxygen storage material. The main reasons may be:Zr4+ ions get into the CeO2 phase, preventing CeO2 crystal aggregation, thereby enhancing the surface area of oxygen storage material, meanwhile Zr4+ ions cause CeO2 crystal defects and increase the ability of oxygen migration within the crystal, thereby enhancing the oxygen storage capacity.5. Ceria-zirconia solid solution mixed with Al2O3 can increase its oxygen storage capacity,which with 40% Al2O3 has the best oxygen storage capacity. The main reasons may be that Al2O3 gets into solid solution, preventing aggregation of CeO2-ZrO2 at high temperature and increasing surface area of the oxygen storage material, thereby enhancing its oxygen storage capacity.7. With the increase of Al2O3 content, the catalytic activity of Pd/CeO2-ZrO2-Al2O3 increases first and then decreases.When Al2O3 content is up to 60%, the three-way catalyst Pd/CeO2-ZrO2-Al2O3 has the best catalytic activity.8. This paper has designed and built a catalyst evaluation device to evaluate the catalytic performance. The device not only can meet for the detection of three-way catalytic activity and oxygen storage capacity, but also can be used to detect diesel catalysts.