化学组装法制备汽车尾气净化催化剂

【作者】 曾佩兰；

【导师】 黄可龙；

【作者基本信息】 中南大学 ， 应用化学， 2003， 硕士

【摘要】 汽车尾气的污染已经引起了人们的普遍关注。汽车尾气的主要污染物可导致酸雨和城市光化学烟雾，严重影响生态环境，危害人体健康。因此治理汽车尾气污染已经成为一项刻不容缓的任务。针对汽车尾气污染源的流动性，人们在汽车岐管内安装催化转化器使污染物在排入大气之前转化为无害的物质，但是汽车冷启动时所造成的污染仍然得不到治理。基于此，利用金属基体热容量小的特点，本研究采用电化学阳极氧化技术制备金属蜂窝载体，再用化学组装法制备汽车尾气净化催化剂力图解决汽车冷启动时的污染问题。 采用电化学阳极氧化技术，以高纯铝箔为原料，在草酸或硫酸电解质中，恒电压下阳极氧化铝箔均可制备纳米氧化铝模板。在制备过程中，我们分别考察了电抛光工艺、氧化时间、氧化电压、电解质种类、体系温度和腐蚀液的体积比等因素对纳米氧化铝孔径的影响，并确定了最佳工艺条件：在0.3mol·L^-1的草酸电解质中，40V的氧化电压下氧化4小时，然后于5％的磷酸溶液中化学刻蚀清洗之后，再在相同的电解体系中氧化2小时，最后于体积比为5：1的6％磷酸和1.8％的铬酸组成的混合腐蚀液中进行腐蚀。 以纳米氧化铝模板（AAMs）为催化剂载体，氯化钯为原料，采用浸渍法制备了Pd-AAMs汽车尾气净化催化剂样品。考察了氯化钯溶液的浓度、浸渍次数、焙烧温度、反应温度及制备工艺对该催化剂的催化活性的影响。研究表明纳米氧化铝模板在1％的氯化钯活性液中浸渍4次，于600℃下焙烧样品，反应温度在140～250℃下，该催化剂的活性都较好，对CO的转化率可达到92％。 以纳米氧化铝模板为催化剂载体，氯化钯和亚硝酸铈为原料采用浸渍法制备了Pd-CeO₂-AAMs催化剂样品，并考察了硝酸亚铈溶液的浓度、气体流量、反应温度对该催化剂活性的影响及该催化剂硕士学位论文摘要的热稳定性。研究发现:随着ceo:含量的增加，Pd一ceoZ^AAMs在低温段的催化活性稍有提高，当反应温度达到200℃以上时，催化活性趋于一致，而且CeO:的加入使得Pd一AAMS的热稳定性也得到大大提高。更多还原

【Abstract】 Pollution of automobile exhaust has already attracted people’s widespread attention. The main pollutant in the automobile exhaust may cause acidic rain and photochemical smog, pollute environment severely and endanger people’s health. Therefore, controlling of automobile exhaust pollution has already become an urgent task today. Aiming at the fluid of the source of exhaust pollution, converter is equipped in the discharging pipe that makes pollutant harmless. However, in the case of cold-start, it is useless. According to this, making use of the characteristics of the small thermal capacity of metal-based supports, metal honeycomb supports are prepared by anodic oxidizing technology and are made them assemble catalytic component of purification of automotive exhaust in order to solve the problem of pollution during the cold start in the research.High purity aluminum foils are used as the starting materials and are anodized by anodic oxidizing technology in the constant voltage. The nanometer anodic alumina membranes (AAMs) were both prepared in the sulfuric and oxalic acid solution. During the preparation of AAMs, the factors affecting its pore diameter, such as technique of electropolishing, anodization time, anodization voltage, the type of electrolyst, temperature in the cell and the proportion of etching solution were investigated, and make sure that the optimal processes were: in 0.3 mol /L oxalic acid under 40V, anode oxidize aluminum foil for 4 hours, then chemical etch in the phosphoric acid solution of which the content is 5%, and then anode oxidize in the same condition for 2 hours, and finally erode in a mixture of 6% phosphoric acid and 1.8% chromic acid, at the volume proportion of 5:1.The Pd-AAMs catalyst samples were prepared by impregnation method, that is,using AAMs and PdCl2 as carriers and active component respectively. The factors affecting the catalytic activities, such asconcentration of PdCl2, times of impregnation, calcinations temperature,reactive temperature etc. have been investigated, when AAMs were immersed in the 1% PdCl2 solution for four times, and then calcined in the 600 C,the catalytic materials for purifying automobile exhaust are finally obtained, and when the optional reaction temperature is the range of 140~250 C of reaction temperature. The conversion rate of CO can arrive 92%.The Pd-CeO2-AAMs catalyst samples were also prepared by impregnation method, in which AAMs, PdCl2 and Ce(NO3)3 are used as starting materials. The factors affecting the Pd-CeO2-AAMs catalytic activities, such as the concentration of Ce(NO3)3, fluid capacity of simulated automobile exhaust and reaction temperature have been investigated. What’s more, their thermal stabilities also have been discussed. The results showed that catalytic activities increased little with the growing of CeO2 under relatively low temperature. When reaction temperature was over 200 C, the contents of CeO2 in the catalysts seemed have no effect on their activities. Moreover, the thermal stabilities of Pd-CeO2-AAMs were improved with the concentrations of CeO2.更多还原