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首页> 外文会议>Innovations in industrial and engineering chemistry : A century of achievements and prospects for the new millennium >Chapter 7 Purification of Automotive Exhaust through Catalysis
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Chapter 7 Purification of Automotive Exhaust through Catalysis

机译：第七章催化净化汽车尾气

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The worldwide effort to reduce the harmful effects of automotive exhaust has witnessed impressive progress during the past 30 years. Driven by the regulatory agencies, emissions have steadily declined and now represent a small fraction of their pre-control values.rnGasoline-powered passenger cars, which comprise a large majority of the US market, emit CO, unburnt HC and oxides of nitrogen (NOx). Starting in 1981, the automobile industry was mandated to sharply reduce the emissions of all three (previously only CO and HC had to be removed). This required "three-way-conversion" (TWC): the simultaneous oxidation of CO/HCs and reduction of NOx, a feat without precedent in the chemical industry. It can only be accomplished by keeping the exhaust gas composition extremely close to the stoichiometric point. Cerium oxide was soon recognized as indispensable to the success of the TWC catalyst, due to its ability to rapidly change oxidation states at the surface. This enables it to "store" and "release" oxygen in response to changes in the gas phase composition. The use of ceria was greatly expanded by the addition of zirconia; the ceria-zirconia was far more thermally stable than ceria itself and allowed the TWC catalyst to survive much higher temperatures.rnDiesel exhaust differs from gasoline exhaust in important respects. It is always "lean" (i.e., net oxidizing) and three-wayrnconversion is thus ruled out. The chief concern is particulate matter, which includes dry soot and a "soluble organic fraction" (SOF), comprised of mainly C_(20)-C_(28). Prior to 2000, attention was mainly focused on SOF conversion, as dry soot emissions could be controlled within the standards by optimizing fuel delivery, air intake systems, and the combustion process. To meet the new emission standards proposed for 2007-2009 in the U.S, Europe and Japan, the diesel particulate filter (DPF) was created, in which the channel wall filters out the soot particles. The latter are burned off, at suitable intervals, by raising the temperature. DPFs were originally limited to trucks and buses, but their proven effectiveness has led to their planned use on passenger cars as well.rnA final topic in diesel aftertreatment is NOx removal. A successful approach, already in place in Europe, is the use of urea, carried on-board as an aqueous solution. Urea hydrolyzes to release NH_3, which is a highly effective agent for converting NOx to N_2.
机译：在过去30年中，全球减少汽车尾气有害影响的努力取得了令人瞩目的进展。在监管机构的推动下，排放量稳步下降，现在仅占其预控制值的一小部分。rn汽油驱动的乘用车（占美国市场的大多数）排放CO，未燃烧的HC和氮氧化物（NOx） ）。从1981年开始，汽车行业被要求大幅度减少这三者的排放（以前只清除了CO和HC）。这需要“三重转换”（TWC）：CO / HCs的同时氧化和NOx的还原，这在化学工业中尚无先例。这只能通过使废气成分非常接近化学计量点来实现。氧化铈由于其快速改变表面氧化态的能力而很快被认为是TWC催化剂成功所不可或缺的。这使其能够响应气相组成的变化而“存储”和“释放”氧气。氧化锆的加入极大地扩展了二氧化铈的使用。二氧化铈-氧化锆比二氧化铈本身具有更高的热稳定性，并允许TWC催化剂在更高的温度下生存。柴油排气在重要方面不同于汽油排气。它始终是“稀薄的”（即净氧化），因此排除了三向转化。主要关注的是颗粒物，其中包括干烟灰和主要由C_（20）-C_（28）组成的“可溶性有机部分”（SOF）。在2000年之前，注意力主要集中在SOF转换上，因为可以通过优化燃料输送，进气系统和燃烧过程将干烟尘排放控制在标准之内。为了满足美国，欧洲和日本针对2007-2009年提出的新排放标准，创建了柴油机微粒过滤器（DPF），其中通道壁过滤掉了烟尘颗粒。通过升高温度以适当的间隔烧掉后者。 DPF最初仅限于卡车和公共汽车，但其行之有效的效果也促使它们计划在乘用车上使用。柴油后处理的最后一个主题是NOx的去除。在欧洲，一种成功的方法是使用随车携带的尿素作为水溶液。尿素水解释放出NH_3，这是将NOx转化为N_2的高效剂。

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