论文总字数：35574字

摘 要

氮氧化物（NO_x）超过硫氧化物成为雾霾的主要无机细粒子，严重危害人体健康，成为国家蓝天保卫战的治理重点。移动源尾气是主要的NO_x排放源，目前主要采用氨气选择性催化还原（NH₃-SCR）脱硝技术，其技术核心是脱硝催化剂。商用柴油机尾气脱硝催化剂均为堇青石负载钒基体系，具有机械强度高、脱硝性能好，耐热耐冲击性能优等特点。但因其活性组分V₂O₅剧毒水溶、高温易挥发，废弃后二次污染，研发环境友好型脱硝催化剂成为柴油机尾气脱硝的紧迫需求。稀土基脱硝催化剂环境友好，脱硝效率高，稳定性好，被国家三部委指定为钒基催化剂的替代品。本文选取代表性CeSnMoO_x/堇青石（CC）和CeSnWO_x/堇青石（CC）催化剂作为研究对象，探究了影响其脱硝活性及催化剂负载强度的因素。研究发现，CeSnMoO_x/CC和CeSnWO_x/CC催化剂的最佳负载量均为10 wt.%，CeSnWO_x/CC比CeSnMoO_x/CC催化剂展现了更好的脱硝活性及更宽的活性温度窗口。此外，较高的焙烧温度（600 °C）有利于提高催化剂与堇青石载体的结合强度，涂敷γ-Al₂O₃涂层亦有利于提高催化剂与载体之间的结合强度及脱硝活性。

关键词：移动源尾气脱硝 选择性催化还原 CeSnMoO_x/CC CeSnWO_x/CC 结合强度

Preparation and properties of cordierite-supported rare earth-based deNO_x catalyst

Abstract

Nitrogen oxides (NO_x) is surpassing sulfur oxides and becoming the main inorganic fine particles of haze, which is seriously endangering human health. The abatement of NO_x is becoming the focus of the national blue-sky defense battle. Mobile source exhaust gas is the main source of NO_x emissions. Ammonia-selective catalytic reduction (NH₃-SCR) deNO_x technology has been mainly applied currently. The core of this technology is the deNO_x catalyst. The commercial diesel engine deNO_x catalysts are cordierite-supported vanadium-based systems, which have the characteristics of high mechanical strength, perfect deNO_x performance, and excellent heat and impact resistance. However, the active component of these systems is V₂O₅, which is toxic, water-soluble, volatile at high temperature, and could cause secondary pollution after being discarded. Considering these factors, the development of environmental-friendly deNO_x catalysts has become an urgent need for diesel engine deNO_x. The rare earth-based deNO_x catalyst is environmental-friendly, has high deNO_x efficiency and good stability, which has been designated as a substitute for vanadium-based catalysts by the three national ministries and commissions. In this paper, CeSnMoO_x/CC and CeSnWO_x/CC catalysts were selected as the research objects to explore the factors that affecting their deNO_x activity and catalyst loading strength. It was found that the optimal loading amount of both CeSnMoO_x/CC and CeSnWO_x/CC catalysts was 10 wt.%. Compared with CeSnMoO_x/CC, CeSnWO_x/CC shows better deNO_x activity and wider active window. In addition, higher calcination temperature (600 °C) is beneficial to improve the binding strength of catalyst and supporter. At the same time, the existence of γ-Al₂O₃ coating greatly improves the binding strength and deNO_x activity between catalyst and carrier.

Keywords: Mobile source deNO_x; SCR; CeSnMoO_x/CC; CeSnWO_x/CC; bonding strength

目录

摘要 I

Abstract II

第一章 绪论 1

1.1 课题背景 1

1.2 脱硝技术 2

1.2.1 NH₃选择性催化还原技术 3

1.2.2 NH₃-SCR脱硝催化剂 5

1.2.3 NH₃-SCR催化反应机理 9

1.3 堇青石负载NH₃-SCR脱硝催化剂研究进展 10

1.3.1堇青石负载脱硝催化剂涂层材料 11

1.3.2堇青石负载脱硝催化剂活性组分 12

1.4 小结 13

第二章 实验方法 15

2.1 化学试剂及药品 15

2.2 实验仪器 16

2.3 催化剂样品制备 16

2.4 催化剂的活性测试 18

2.5 催化剂的强度测试 19

第三章 结果与讨论 20

3.1 催化剂的脱硝活性 20

3.2 催化剂的负载强度 25

第四章 结论与展望 30

4.1 结论 30

4.2 展望 30

参考文献 32

致谢 37

第一章 绪论

1.1 课题背景

目前，大气污染问题日益严峻，亟待解决。大气污染大多来源于燃煤发电厂、钢铁厂、水泥厂等工业生产中。这些污染物主要由颗粒物、氧化硫和氮氧化物组成。其中，NO_x的治理（脱硝）成为大气污染治理的重点^[1][吴书昊, 2018 #2]。据统计，化石燃料的燃烧产生近5%的NO₂和95%的NO^[2]。此外，氮氧化物（NO_x）的存在形式还有很多种，例如NO₃、N₂O、N₂O₃和N₂O₄等等。排放的氮氧化物分为三种类型：第一种为热力型氮氧化物。热力型氮氧化物是通过氧气在高温下氧化大气中的氮而形成；第二种为燃料型氮氧化物。当燃料中的含氮化合物在低温下作为挥发物释放并部分转化为NO时，燃料中含氮化合物氧化形成燃料型氮氧化物；第三种为快速型氮氧化物。碳氢化合物（HC）与分子氮在富燃料、低温的条件下，在较短的时间内燃烧产生快速型氮氧化物。氮氧化物是燃料燃烧产生的主要大气污染物之一^[3]。氮氧化物的排放会引起一系列的健康和问题，如眼睛和喉咙的刺激，胸闷，恶心和头痛，以及环境问题，如臭氧的破坏，酸雨，烟雾，光化学烟雾和温室气体的排放，因此，必须减少和控制污染物的排放，尤其是氮氧化物的排放（脱硝），以提高生活质量^[4]。

相比于其他脱硝技术，氨气选择性催化还原（NH₃-SCR）脱硝技术由于其脱硝效率高，稳定性好，技术成熟等优点已经成为柴油车尾气净化领域发展方向的重要技术^{[5, 6]}。NH₃-SCR技术关键在于研发高效、环保、宽广的工作温度以及稳定的脱硝效率的催化剂。

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