【作者】 张敏；

【导师】 刘勇军； 李新；

【作者基本信息】 四川大学 ， 环境工程（专业学位）， 2021， 硕士

【摘要】 氮氧化物（NO_X）是我国主要大气污染物,它会导致一系列环境污染问题,如光化学烟雾、酸雨和温室效应等,对环境和人类健康造成巨大危害,其中一氧化氮（NO）是NO_X中的主要污染物。NH₃选择性催化还原技术（NH₃-SCR）是目前脱除NO最有效的方法,其核心是催化剂。目前工业应用的V₂O₅-WO₃/Ti O₂传统脱硝催化剂脱硝效率高,但存在活性组分V₂O₅有毒且易挥发和活性温度高、温度窗口窄（300～400℃）等缺点。近年研究表明,锰基催化剂具有良好的SCR活性,具备工业化应用潜能,但在实际烟气中SO₂、H₂O等毒物会降低锰基催化剂的脱硝活性甚至导致催化剂失活。因此,开发高SCR活性、宽温度窗口、高抗硫性的锰基脱硝催化剂是目前研究的新方向。本文首先用沉积沉淀法制备了不同锰负载量的Mn/Ti O₂催化剂,筛选出最佳锰负载量,再制备了Fe-Mn/Ti O₂、Ce-Mn/Ti O₂催化剂,通过XRD、XPS等表征分析,选择脱硝活性更高的Fe-Mn/Ti O₂催化剂,最后将不同比例Ce元素负载于Fe-Mn/Ti O₂催化剂,筛选出最优比例的Fe-Mn-Ce_0.1/Ti O₂催化剂,最后研究SO₂预处理之后Fe-Mn-Ce_0.1/Ti O₂和Fe-Mn/Ti O₂催化剂抗硫性能变化。实验结果表明:（1）25wt%为最佳Mn负载量。25wt%Mn/Ti O₂催化剂显示出最优异的脱硝活性,反应温度为130℃时NO去除率达到90%,且在130～280℃的温度窗口内保持着>90%的NO去除率。（2）助剂Fe和Ce的引入可促进Mn/Ti O₂催化剂的脱硝活性,Fe为最佳掺杂助剂。Ce、Fe的引入可促进活性组分Mn高度分散,增加活性位点。Fe-Mn/Ti O₂催化剂相比Ce-Mn/Ti O₂和Mn/Ti O₂催化剂具有更优异的脱硝活性和更宽的反应温度窗口。一方面,Fe的引入增强了催化剂的酸-氧化还原性能,另一方面Fe的引入促进Mn物种向表面迁移,在表面形成更多高价锰,促进SCR反应进行。（3）Fe:Mn（摩尔比）=1:1为最佳掺杂比例。Fe-Mn/Ti O₂催化剂显示出最优异的脱硝活性,130℃时脱硝效率达到90%。随着Fe掺量的增加,Fe_X-Mn/Ti O₂催化剂表面酸含量增加,促进SCR反应进行。（4）Ce掺量为0.1时制备的Fe-Mn-Ce_0.1/Ti O₂催化剂具有最佳脱硝活性,在102℃时NO去除率达到90%。且该催化剂有最宽高活性温度区间,在102～320℃温度范围内维持>90%的NO去除率。物理化学表征表明,一方面,Ce的引入增大催化剂表面晶格氧含量,增大其储氧量,提高其催化氧化性能。另一方面,Ce的引入使得催化剂表面出现多种酸性位点均匀分布,使其在较宽温度窗口能保持高活性。（5）煅烧温度对催化剂脱硝活性影响不明显,但是显著影响催化剂的抗硫性。煅烧温度为450℃时制备的催化剂具有最优异的抗硫性能,中毒后Fe-Mn-Ce_0.1/Ti O₂-450催化剂在200℃反应温度下NO去除率仍可达85%。（6）Fe-Mn/Ti O₂催化剂在中毒后活性明显下降,在整个反应温度区间内NO去除率均未超过80%。在引入Ce对催化剂进行改性后,Fe-Mn-Ce_0.1/Ti O₂催化剂相比于Fe-Mn/Ti O₂催化剂抗硫性得到明显提高,中毒后的Fe-Mn-Ce_0.1/Ti O₂催化剂在175～325℃温度区间内保持>80%的NO去除率。中毒后催化剂比表面积下降、氧化还原性能下降、表面形成难以参与SCR反应的强吸附NH₃,使得催化剂活性下降。此外,理化性质改变抑制表面吸附氧对被消耗晶格氧的补充,进而造成催化剂活性下降以及活性温度窗口变窄。Ce的引入在一定程度上抑制了中毒对催化剂性质的改变,进而削弱了中毒对催化剂催化活性的影响。更多还原

【Abstract】 Nitrogen oxide（NOx）is one of the main air pollutants in China.It will lead to a series of environmental pollution problems,such as photochemical smog,acid rain and greenhouse effect,and cause great harm to the environment and human health,including nitric oxide（NO）is the main pollutant in NOx.NH₃ selective catalytic reduction（NH₃-SCR）is the most effective method to remove NOx,and its core is catalyst.At present,the traditional V₂O₅-WO₃/Ti O₂ catalyst has high denitration efficiency,but it has some disadvantages,such as the active component V₂O₅ is toxic and volatile,the active temperature is high,and the temperature window is narrow（300～400℃）.Recent studies have shown that manganese based catalysts have good SCR activity and potential for industrial application.However,in the actual flue gas,SO₂,H₂O and other toxins will reduce the denitration activity of manganese based catalysts,and even lead to catalyst deactivation.Therefore,it is a new research direction to develop Mn based denitrification catalysts with high SCR activity,wide temperature window and high sulfur resistance.In this research,Mn/Ti O₂ catalysts with Different Mn loading were prepared by deposition precipitation method,and the best Mn loading was selected.Then Fe-Mn/Ti O₂ and CE-Mn/Ti O₂catalysts were prepared.Through XRD and XPS characterization,Fe-Mn/Ti O₂ catalysts with higher denitration activity were selected.Finally,Fe-Mn-Ce_0.1/Ti O₂ catalysts with different Ce loading ratios were selected,Finally,the sulfur resistance of Fe-Mn-Ce_0.1/Ti O₂ and Fe-Mn/Ti O₂ catalysts after SO₂ pretreatment was studied.The experimental results show that:（1）25wt%is the best Mn loading.25wt%Mn/Ti O₂ catalyst showed the best denitrification activity.The no removal rate reached 90%at 130℃,and maintained more than 90%in the temperature window of 130～280℃.（2）The introduction of Fe and Ce can promote the denitration activity of Mn/Ti O₂catalyst,and Fe is the best doping promoter.The introduction of Ce and Fe can promote the high dispersion of Mn and increase the active sites.Compared with Ce-Mn/Ti O₂ and Mn/Ti O₂,Fe-Mn/Ti O₂ catalyst has better denitration activity and wider reaction temperature window.On the one hand,the introduction of Fe enhanced the acid redox performance of the catalyst;on the other hand,the introduction of Fe promoted the migration of Mn species to the surface,forming more high valence manganese on the surface,which promoted the SCR reaction.（3）Fe:Mn（mole ratio）=1:1 is the best doping ratio.Fe-Mn/Ti O₂ catalyst showed the best denitration activity,and the denitration efficiency reached 90%at 130℃.With the increase of Fe content,the surface acid content of Fex-Mn/Ti O₂ catalyst increased,which promoted the SCR reaction.（4）The Fe-Mn-Ce_0.1/Ti O₂ catalyst with 0.1 Ce content has the best denitration activity,and the no removal rate reaches 90%at 102℃.Moreover,the catalyst has the widest active temperature range and maintains no removal rate of>90%in the temperature range of 102～320℃.Physical and chemical characterization showed that,on the one hand,the introduction of Ce increased the lattice oxygen content on the surface of the catalyst,increased its oxygen storage,and improved its catalytic oxidation performance.On the other hand,the introduction of Ce makes a variety of acidic sites uniform Ly distributed on the surface of the catalyst,which can maintain high activity in a wide temperature window.（5）The calcination temperature has no obvious effect on the denitration activity of the catalyst,but has a significant effect on the sulfur resistance of the catalyst.The results show that the catalyst calcined at 450℃has the best sulfur resistance.After poisoning,the NO removal rate of Fe-Mn-Ce_0.1/Ti O₂-450 catalyst can still reach 85%at 200℃.（6）The activity of Fe-Mn/Ti O₂ catalyst decreased obviously after poisoning,and the no removal rate did not exceed 80%in the whole reaction temperature range.Compared with Fe-Mn/Ti O₂ catalyst,the sulfur resistance of Fe-Mn-Ce_0.1/Ti O₂ catalyst was significantly improved after the introduction of Ce.The no removal rate of Fe-Mn-Ce_0.1/Ti O₂catalyst after poisoning was more than 80%in the temperature range of 175～325℃.After poisoning,the specific surface area of the catalyst decreased,the redox performance decreased,and the surface formed strong adsorption NH₃,which was difficult to participate in SCR reaction.In addition,the change of physicochemical properties inhibited the supplement of absorbed oxygen to consumed lattice oxygen,resulting in the decrease of catalyst activity and narrowing of activity temperature window.To some extent,the introduction of Ce inhibited the poisoning effect on the properties of the catalyst,and then weakened the effect of poisoning on the catalytic activity of the catalyst.更多还原