论文总字数：26941字

摘 要

氮氧化物（NOx）是一种危害极大的污染性气体，引发了一系列环境问题。人们尝试多种治理技术来降低NOx排放，而NH₃选择性催化还原技术（NH₃–SCR）是现阶段商业化应用最成熟的脱硝技术。CeO₂-TiO₂催化剂的脱硝活性高，产物的选择性强，具有很好的开发前景，但也存在脱硝温度较高，抗硫性较差等缺点。为解决这些问题，本课题研究了SnO₂掺杂对CeO₂-TiO₂催化剂催化性能的影响，并对改性后的催化剂进行了一系列的表征分析，得到了以下结论：

（1）适量的Sn掺杂可以改善催化剂在中高温区间的脱硝效率并拓宽催化剂的温度窗口。配比为Ce_0.2-Sn_0.1-Ti的催化剂脱硝效率最高，在300℃左右时可达95%以上，且具有最宽的温度窗口。但过多的SnO₂反而会抑制催化剂的催化活性。

（2）改性后的催化剂抗水抗硫性明显增强，Ce_0.2-Sn_0.1-Ti 催化剂在SO₂(100ppm)和H₂O(5vol%)混合存在的环境下仍保持75%左右的催化活性，并能在SO₂和H₂O除去后恢复至90%。热重-差热分析（TG-DSC）结果显示Sn的掺杂抑制了NH₃和SO₂间的氧化还原反应并降低了硫酸盐的形成，从而增强了催化剂的抗硫性。

（3）掺杂的SnO₂与CeO₂形成了固溶体，降低了CeO₂的结晶度，改善了活性组分在载体表面的分散程度。改性后催化剂颗粒的比表面积更大，且粒径更均匀，无明显团聚现象。催化剂的孔结构也得到了改善，这有利于降低气体在催化剂中的扩散阻力，促进反应气体的吸附和产物气体的脱附，有助于SCR反应的进行。

（4）Sn离子促进了不同价态的铈离子相互转化，同时增加了催化剂表面的氧空位数量，提升了催化剂的还原能力。

（5）原位DRIFT光谱显示Sn的引入增加了催化剂表面的酸性位点，使催化反应更容易进行，提高了NOx的消耗速率和反应活性。SnO₂的掺入使得CeO₂中Ce³ 数目增加，影响了晶格内电子的平衡，导致晶格出现空位等缺陷，从而提供了酸性位点。掺入SnO₂后，催化剂颗粒的比表面积增大，暴露出更多的酸性位点，这也是催化剂酸位增多的原因。

关键词：NH₃-SCR；Ce-Ti；催化剂；SnO₂掺杂；

Abstract

Nitrogen oxides (NOx) is a very harmful polluting gas. NH₃ selective catalytic reduction technology (NH₃–SCR) is the most commercialized denitration technology. CeO₂-TiO₂ catalyst has high denitration activity, strong product selectivity, and good development prospects, but it also has shortcomings such as higher activation temperature, poor water and sulfur resistance. In order to solve these problems, this subject studied the influence of SnO₂ doping on the catalytic performance of CeO₂-TiO₂ catalyst, and carried out a series of characterization analysis on the modified catalyst, and got the following conclusions:

(1)A proper amount of Sn doping can improve the denitration efficiency of the catalyst in the middle and high temperature range and widen the temperature window of the catalyst. The catalyst with the ratio of Ce_0.2-Sn_0.1-Ti has the highest denitration efficiency, which can reach more than 95% at about 300℃, and has the widest temperature window. But too much SnO₂ will inhibit the catalytic activity of the catalyst.

(2) The water and sulfur resistance of the modified catalyst is obviously enhanced. The Ce_0.2-Sn_0.1-Ti catalyst still maintains about 75% of its catalytic activity in the environment where SO₂ (100ppm) and H₂O (5vol%) are mixed and can recover to 90% after SO₂ and H₂O removed. TG-DSC analysis showed that the doping of Sn inhibited the redox reaction between NH₃ and SO₂ and inhibited the formation of sulfate, thereby enhancing the sulfur resistance of the catalyst.

(3) The doped SnO₂ and CeO₂ form a solid solution, which reduces the crystallinity of CeO₂ and improves the degree of dispersion of the active component on the surface of the carrier. After modification, the specific surface area of the catalyst particles is larger, and the particle size is more uniform, without obvious agglomeration. The pore structure of the catalyst has also been improved, which is beneficial to reduce the diffusion resistance of the gas in the catalyst, promotes the adsorption of reaction gas and the desorption of product gas, and helps the SCR reaction.

(4) The doped SnO₂ induces the distortion of the CeO₂ lattice, resulting in a series of vacancy defects, and promotes the mutual conversion of tin ions and cerium ions of different valence states, and enhances the reduction ability of the catalyst.

(5) In situ DRIFT spectroscopy shows that the introduction of Sn increases the acid sites on the catalyst surface, makes the catalytic reaction easier to proceed, and improves the NOx consumption rate and reaction activity. The incorporation of SnO₂ increases the number of Ce³ in CeO₂, which affects the balance of electrons in the crystal lattice, resulting in defects such as vacancies in the crystal lattice, thereby providing acid sites. After doping with SnO₂, the specific surface area of the catalyst particles increases and more acid sites are exposed, which is also the reason for the increase of catalyst acid sites.

Keyword: NH₃-SCR; Ce-Ti; Catalyst; SnO₂ doping

目 录

第一章 绪论 1

1.1 NOx的来源和危害 1

1.2 NOx的控制技术 1

1.3 NH₃选择性催化还原技术 1

1.4 SCR催化剂的研究进展 2

1.4.1活性组分 2

1.4.2载体 3

1.5 铈钛催化剂的研究进展 4

1.6 论文的研究目的及研究内容 4

第二章 Sn掺杂Ce-Ti催化剂的制备与活性测试 6

2.1 催化剂的制备 6

2.2 脱硝活性测试 6

2.3 脱硝活性分析 7

2.4 SO₂中毒测试 7

2.5 本章小结 8

第三章 Sn掺杂Ce-Ti催化剂的表征与分析 10

3.1 晶相结构测试 10

3.2 微观结构表征测试 11

3.3 比表面积表征测试 11

3.4 还原能力表征测试 12

3.5 表面酸量表征测试 13

3.6 热重-差热分析测试 14

3.7 原位机理表征测试 14

3.8 本章小结 16

第四章 总结与展望 18

4.1 全文总结 18

4.2 工作展望 18

参考文献 19

致谢 22

第一章 绪论

1.1 NOx的来源和危害

NOx会造成一系列严重的环境污染，是大气主要污染物之一。在自然环境下，空气中少量氮气会被氧化成NOx，但这种NOx含量极少，对环境的影响也较小。相比之下，人类活动排放的烟气则是NOx的主要来源。

随着我国近年来的发展，工业化程度逐年提高，煤炭燃料的消耗也在不断增加，随之产生的有害气体的排放问题也日益严重。近年来，NOx已成为我国的首要污染物。《中国环境状况公报（2015 年）》^[1]显示，以燃烧化石燃料为主的电厂、工厂等固定源是NOx的主要来源，机动车等移动源次之。

人类活动产生的NOx对人们的生命安全，日常活动，经济建设以及生态环境带来了极大的危害。NO在空气中易转化成NO₂。NO₂是一种呼吸道刺激性气体，会引发肺水肿、支气管炎等疾病。长期暴露在高浓度的NO₂环境下，会给呼吸系统带来极大的负担。此外，NOx也是酸雨的主要诱因之一。酸雨会化土壤并污染水体，还会腐蚀建筑物，严重危害着公共安全。因此，控制NOx的排放，改善大气环境刻不容缓。

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