Study On Reduction Technology Of NO_x Emitted And Sr Catalysts By Gasoline Engine

Normal vehicle exhaust includes HC, NO_x,CO, and PM etc. With the development of combustion technology, NO* becomes the main pollution source in modern city road. At present, three-way catalyst is widely used to purify vehicle exhaust. However, it does not work under all conditions, but only strict air-fuel delivery ratio conditions. When A/F >14.7, the effect of NO_x reduction weakens rapidly, that is, three-way catalyst will lose reduction ability. In addition, with the rapid development of world automobile industry, the production of three-way catalyst will consume a lot of precious metal. Unfortunately, Rh, Pt, which are mainly distributed in South Africa and former Soviet Union ,are not rich in world area. As a result, the shortage of supply and high price of them make experts take various actions to control the use of Pt and Rh. Therefore, how to purify and catalyze NO_x under all air-fuel delivery ratio conditions with the reduction of Pt and Rh becomes a pressing problem, and also an important task in the field of vehicle exhaust catalyst purification.The combustion process of engine is analysed in this paper ,then established the model of pressure,temperature ,volume,quality and so on.While the chemical reacter theory of cylinds is studied in this paper too,and established the emission material arithmeric of oil engine.Under the condition of all air-fuel delivery ratio and temperature, engine emission experiments show that putting into 20 wt.% Ce on Ce/Al₂O₃ catalyst at the temperature of 500℃, the maximum conversion ratio is 28%. When Ce/Zr is 2.5, the maximum conversion ratio of Ce-Zr/Al₂O₃ catalyst is 37% at 450℃.Putting 3 wt.% Sr at 450℃,the maximum conversion ratio is 39%. Study illustrates that adding Ce,Zr and Sr, Ce-Zr-Sr/Al₂O₃ catalytic ability will be the best to NO_x,at high temperature, NO_x conversion ratio reaches the peak.Further study Ce-Zr-Sr/Al₂O₃ catalytic ability, adding noble metal Pt-Rh into Ce-Zr-Sr/Al₂O₃,experimental shows that, in Pt-Rh/Ce-Zr-Sr/Al₂O₃,among Pt,Rh and Ce-Zr-Sr/Al₂O₃,exist synergistic effect, this will promote catalytic ability, especially when Rh/Pt is 0.25, Rh-Pt content is 0.5 wt.%.Further study on the addition of precious metal Pt-Rh into Ce-Zr-Sr/Al₂O₃,shows that in Pt-Rh/Ce-Zr-Sr/Al₂O₃,there exists synergistic effect among Pt,Rh and Ce-Zr-Sr/Al₂O₃,which will promote catalytic ability, especially when Rh/Pt is 0.25, Rh-Pt content is 0.6 wt.%, and Sr content is 3 wt.%, the catalytic activity performs best. Not only in low or wide temperature condition but also in higher temperature, Pt-Rh/Ce-Zr-Sr/Al₂O₃ can show high specific surface area raio and excellent stability. It is considered as the best catalyst, which has a promising industry application prospects.The conclusion could be used for NO_x catalyst optimize design at all air-fuel delivery ratio condition ,and provide impmant theory value for catalyst's further study.Experimental data and theory analysis show that Sr can partly replace Rh and Pt.Adding 3 wt.% Sr can increase convert efficiency of NO_x,especially under low temperature. At first, single metal such as Ce/Al₂O₃,Zr/Al₂O₃,Sr/Al₂O₃ and Fe/Al₂O₃ catalysts are discussed in this paper. Experiments show that catalytic reduction ability of Ce/Al₂O₃ to NO_x is higher than others. When adding Zr,Sr and Fe into Ce/Al₂O₃,study shows that the efficiency of conversion is higher. While put into Sr and Fe, Ce-Zr-Sr/Al₂O₃ performs best, but Fe may reduce this ability. Hence, this paper takes Ce-Zr-Sr/Al₂O₃ as the example to study this basis theory.Study on response condition which has been adopted to low Pt-Rh shows that low Pt-Rh catalyst can purify not only NO_x,but also HC, CO, whose highest conversion rates are 65% and 52% respectively. Experiments show that the higher the A/F, the lower NO_x conversion efficiency will become, the higher conversion efficiency of HC, CO will be. When A/F>15,conversion rate of HC and CO decreases.Based on catalytic converter response theory, responding velocity formula are discussed in this paper, and a maths model about catalytic responding system has been established. Then the author uses computer and value imitation to design catalytic converter, and establishes the math model under the low activity by adding various content precious metals such as Pt-Rh, Sr etc. Consequently, the author succeeds in getting the theoretical best value under various conditions, and applies it to optimizing design for all air-fuel delivery ratio.