摩托车排气催化净化技术研究
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摘要
近年来,随着我国汽车工业的迅速发展,机动车保有量迅速增加,我国的许多大城市也已由煤烟型污染向混合型(煤烟—尾气型)污染转化,机动车排放已成为我国大城市大气污染的一个主要来源。因此,控制汽车排放,治理城市大气污染已成为我国大城市刻不容缓的重要任务。
     控制汽车排放污染的方法和手段有多种,如使用电动汽车、采用代用燃料、燃油添加剂、安装附加装置、改善发动机、机内净化或机外净化等,其中采用催化剂技术进行汽车排气后处理是目前减少汽车排放污染的主要措施。目前,汽车排放控制采用的负载型催化剂的载体大多是由以堇青石为主要成分的蜂窝状陶瓷为第一载体和以γ-Al_2O_3为基质的第二载体即涂层所组成;涂层为活性组分提供了大的表面积,从而能够大大地提高催化剂的性能;而催化剂的稳定性在很大程度上由载体涂层的稳定性所决定;制备催化剂的关键之一就是将涂层均匀地固定在载体的内表面,因此,载体涂层在整个催化剂的研究中占有重要的地位,是机动车尾气催化净化课题研究内容中相当重要的一部分,也是本论文主要研究对象。
     本论文研究的催化转化器是以堇青石蜂窝陶瓷为第一载体、γ-Al_2O_3为第二载体、稀土钙钛矿型复合氧化物为催化剂,并且主要探讨了影响涂层负载及催化剂负载的各种因素,以期得到涂层负载及催化剂负载的最佳值,以及得到该值时需要满足的条件。
     综合试验结果,得到结论如下:(1)胶液的触变性及固含量对涂层负载量均有影响,因此,凡是影响胶液触变性的因素就可影响涂层负载量,而胶液固含量则是影响蜂窝陶瓷涂层负载量的最大因素。固含量在一定条件下,一定范围内变化时,胶液具有触变性,且固含量越高,胶液的触变性越明显;(2)负载涂层及催化剂所需的焙烧温度对涂层的相结构及稳定性有一定的影响;(3)涂层的负载量是影响催化剂负载量的主要因素。涂层的涂覆采用溶胶-凝胶法;(4)催化剂的负载采取多组分共浸渍的方法,催化剂在涂层上是以微晶的钙钛矿形式存在,其分子式为(La_(0.8)Sr_(0.2)MnO_3;(5)摩托车排气净化效果测试显示:该催化器对尾气中的HC和NO_x有明显的催化效果,对尾气中HC化合物和NO_x的催化转化效率分别达43.5%和56.1%,净化后的尾气排放符合国家排放标准,其起燃温度T_(50)为250~350℃。
In recent years the volume of automotive possess has increased quickly with rapid development of industry in our country. The pollution form of our many cities has changed from coal-smoke pollution to mixed pollution (coal-smoke &. tail gas). The emission of automotive tail gas has been the major source of city air pollution. So controlling the automotive exhaust is a important task which brooks no delay.
    There are many means of controlling the automotive exhaust gas. At present time catalytic converter is one of the major way of them to purify automotive exhaust. At the moment, the carrier of catalysts used on controlling of the automotive exhaust almost is made up of cordierite honeycomb carrier which as the first carrier and Y-Al2O3 which as the second carrier. It can enormously increase the catalysts performs because the washcoat offers bigger surface area for catalysts. So the stability of catalysts is decided to a great extent on the stability of the carrier coat. It is one of the key to preparing catalysts that we must fix the washcoat on the inside surface of carrier. So the carrier coat occupies an important place in the whole research of catalysts. It is an important part of the study on purifying automotive exhaust with catalysts. It's also a main object of study in this paper.
    The TWC (three way catalysts) which studied in this paper is made up of three partstcordierite honeycomb carrier which as the first carrier, Y -Al2O3 which as the washcoat and PTO which as catalytic agent. The factors to the loading of the washcoat and the catalysts have been mainly discussed. Some conclusion can be drawn through synthesizing the result of the experiment. The
    
    
    main results are: (1) The most important factor to the loading of the ceramic honeycomb washcoat is the solid of the dispersion. Under given conditions, the sol has thixotropy property when the solid content of dispersion changed in a certain range. It is more apparent with the increase in the solid content of the dispersion. (2) The coat and the catalysts are roasted on a certain temperature which affects the stability of the carrier coat. (3) The main factor to the loading of the catalysts is the loading of the washcoat. The technology of coating is Sol-Gel. (4) The catalysts were prepared by impregnation method. The catalysts' molecular formula is (Lao.gSro.i) MnOs. (5) The results of test indicate that this three way catalysts has a certain catalytic activity for HC and NOx. When the temperature reached 250~350癈, this three way catalysts' catalytic efficiency achieves 43.5% and 56.1%.
引文
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