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机动车(包括汽车、低速汽车、摩托车、挂车和拖拉机等)尾气排放的污染物,如一氧化碳(CO)、未完全燃烧的碳氢化合物(HC)、氮氧化物(NO和NO2,统称NOx)和颗粒物PM(由碳黑Soot内核及其表面吸附的可溶性有机物构成)等,是大气污染的重要来源,也是造成细颗粒物(PM2.5)、臭氧(O3)和光化学烟雾等污染的重要原因。作为汽车尾气污染的典型案例,发生于1940年至1960年间的美国洛杉矶光化学烟雾事件推动了1970年版美国《Clean Air Act(清洁空气法)》的出台,以及1975年将催化净化器引入到汽车尾气处理中[1]。
自2009年以来,我国已连续十一年成为世界机动车产销第一大国,汽车是机动车污染物排放总量的主要贡献者,其排放的CO、HC、NOx和PM等4项主要污染物均超过机动车排放的90%[2]。济南市2017年大气污染源解析结果表明,机动车排放对济南市PM2.5的分担率为32.6%,居各项来源之首,排放的NOx占济南市总排放的65.5%,是第一大贡献源,汽车尾气污染对我国大中城市环境空气质量的影响尤为严重,已直接威胁人民群众的健康和生活[3]。汽油车(燃料为汽油)在机动车中占比较高,是我国乘用车的主要形式,由中国汽车工业协会、社会科学文献出版社等共同发布的《汽车工业蓝皮书:中国汽车工业发展报告(2020)》表明,2019年乘用车占我国该年汽车销量的83.2%,已连续8年超过80%,抓好汽油车尾气污染治理是城市机动车尾气污染控制的关键环节[4]。
面对汽车尾气污染的严峻形势及国家的紧迫要求,本文首先简要介绍了汽油车划时代技术—三效催化剂(three way catalysts,简称TWC)的基本原理,接着回顾了世界(美国为代表)治理汽车尾气45年的发展历史,特别是近20年来我国在TWC方面的技术进步和实践,然后重点介绍了稀土储氧材料、载体和涂覆技术、密偶催化剂和四效催化剂等方面的进展,最后对TWC技术的未来和更环保节能的汽油车尾气后处理技术,进行了展望和畅想。
汽车尾气三效催化剂研究和应用40年
40 years of research and application of three-way catalysts for gasoline automobiles
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摘要:
汽车尾气污染已成为我国大气污染的重要来源,是大气污染防治的重中之重。三效催化剂(TWC)是汽油车和天然气车尾气治理的商业化技术,也是在公众产品市场上使用催化技术的最显著成就之一,对汽车尾气污染物减排具有划时代的重大意义。本文首先简要介绍了TWC的基本原理,回顾了世界(美国为代表)治理汽车尾气40多年的发展历史,特别是近20年来我国在TWC方面的技术进步和实践,然后重点介绍了稀土储氧材料、载体和涂覆技术、密偶催化剂和四效催化剂等进展,最后针对未来低油耗和低CO2排放的汽车需求,展望了未来的TWC和稀燃发动机尾气催化净化技术。
Abstract:Automobile exhaust has become an important source of air pollution in China, which is the key point for air pollution control. The commercial technology for treatment of automobile exhaust from gasoline and natural gas engines is three-way catalyst (TWC), the most remarkable achievement of catalysis application in the public market, implying an unprecedented significance for pollutant removal. Herein, the basic theory of TWC is first introduced followed with a chronological review of forty-years development of TWC in the world, and especially twenty-years R&D in China. Then, recent progresses on oxygen storage materials based on rare-earth oxides, honeycomb supports, coating techniques, close-coupled catalysts and four-way catalysts are highlighted. Finally, the prospective TWCs and catalytic technologies for lean-burn engines with low gasoline consumption and CO2 emission are proposed.
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表 1 蜂窝陶瓷的物理性能
Table 1. Physical properties of honeycomb substrates
目数/cpsi
Mesh number壁厚/mm
Wall thickness壁厚/ mil
Wall thickness几何表面积/(m2·L−1)
Geometric surface area开口面积率/%
Open facial area200 0.305 12 1.8 68.9 300 0.125 5 2.5 83.4 400(Ceramic) 0.101 4 2.9 84.6 400(FeCrAl) 0.04 1.6 3.2 92 600 0.076 3 3.6 85.8 750 0.063 2.5 4.0 86.8 900 0.051 2 4.4 88.4 蜂窝陶瓷数据来自山东奥福环保科技股份有限公司. 表 2 上、下给料涂覆适用性对比
Table 2. Comparison of applicability for upper- and down-feed coating
上给料涂覆Upper-feed coating 下给料涂覆Down-feed coating 每次涂覆量 高涂覆量15%—30%、精度高 低涂覆量3%—15%、精度较高 涂覆工艺 定量给料、真空抽吸 喷射给料、蜂窝反转、真空抽吸 对浆液要求 含固量高的粘稠浆料、流动性好 含固量低的稀薄浆料、流动性好 适合加工的催化剂 TWC、SCR等 GPF、DPF等 -
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