【作者】 赵冬；

【导师】 杨剑；

【作者基本信息】 重庆大学 ， 工程硕士（冶金工程领域）（专业学位）， 2016， 硕士

【摘要】 日益恶化的环境使大气污染防治问题越来越受到重视,日益严格的NOx排放标准给大气污染治理提出了更高的要求。目前应用最为广泛的V2O5-WO3/TiO2系SCR催化剂越发无法适应新的脱硝环境,无法满足新的脱硝性能需求。探索出新型烟气脱硝技术和烟气脱硝催化剂已迫在眉睫。本文通过两个方面制备出新型催化剂:1、利用纳米结构优势,从催化剂微观结构优化催化性能。2、利用最具脱硝潜力的Mn、Ce氧化物作为活性组分替代V,增强催化剂活性。首先,采用水热法制备纳米结构的CeO₂催化剂。通过反复实验校正,最终制备出纳米粒子和纳米棒状CeO₂催化剂。以商用CeO₂作为参比,研究了结构对催化剂性能的影响。结果表明,催化剂微观粒子越小,催化性能越强,但抗高温失活性能有所下降。对催化剂进行BET表征发现,纳米结构能够明显增大催化剂比表面积,但大部分为1-2nm的微孔结构,对催化性能没有明显的提升作用。利用XPS、NH₃-TPD和电镜表征各催化剂后发现,纳米棒状CeO₂表面具有最多的酸性位和表面吸附氧。电化学性能测试方面,纳米棒状CeO₂具有更多的活性分子,使得棒状催化剂能够在低温和中高温区表现出最好的催化性能。但也由于粒子较小,对温度的敏感性比较高,更加容易高温失活。其次研究了Mn负载对催化剂性能的影响。同样利用水热法,以KMnO4为原料,将Mn负载到了纳米结构CeO₂表面。电镜结果显示,Mn是以包裹的形式负载到CeO₂表面。Mn负载后催化剂微观离子变大,增大了催化剂的孔径和比表面积,一定程度上促进了催化性能的提升。CeO₂基体形貌几乎没有改变,MnOx在表层以片状结构存在,且呈现+2、+3和+4多种价态。Mn负载后催化剂表现出了良好的低温催化活性,同时降低了高温失活效应的起始温度。通过电化学分析知道Mn具有更强的氧化还原性能和循环性能,负载量比较大的纳米棒状催化剂,表现出了更好的催化剂活性。最后研究了催化剂中Mn、Ce之间的协同作用机理。实验对比了负载前后催化剂和纯MnOx的脱硝性能。结果显示,复合催化剂性能不仅高于纯纳米CeO₂,还表现出了比纯MnOx更高的催化活性,证明了催化剂不同成分间协同作用的存在。复合催化剂的热重分析结果同样证明了Mn、Ce之间存在明显的协同效应。根据Mn、Ce催化剂的催化机理,分析得出了复合催化剂脱硝协同作用机理:Mn氧化物充当活性物质,通过自身氧化还原的循环作用完成脱硝反应;Ce氧化物作为助催化剂,以强氧化性能促进MnOx的氧化,以高的储氧能力为催化反应补充吸附氧,自身被MnOx还原。还原得到的Ce2O3经过O2氧化为CeO₂,并进一步转化O2为吸附氧。更多还原

【Abstract】 Serious environmental problems attracted more attention in the past few decades. Nowadays, increasingly stringent pollutant emission standard is putting forward a higher requirement for Air Pollution Control. The V2O5-based catalyst, which is most widely used in denitration unit, can`t meet the new requirement of new catalyst performance and the optimal active temperature, and it`s necessary to develop new denitration technology and new catalyst. In this paper, the new catalyst was prepared from two aspects. Firstly, nanostructure was introduced to improve the microstructure of catalyst. Secondly, MnOx and CeO₂, which are the greatest potential active agents, were introduced to improve catalytic activities.Firstly, nano-CeO₂ was prepared by hydrothermal method. CeO₂ nanoparticles and nanorods were successfully prepared after multiple correction experiments. Influence of the nano-CeO₂ texure on catalytic performance was studied in this paper, where commercial CeO₂ as the reference. The results showed that, the smaller the particle was, the higher catalytic activities it showed, but the easier to deactivate at high temperature. The BET results showed that nanostructure could enlarge specific surface area, but most of pores are micropore（1-2nm）, which have no obvious effects on improving catalytic activity. The test results of XPS、NH₃-TPD and SEM showed that there are more acid sites and adsorbed oxygen on the surface of CeO₂ nanorods. CeO₂ nanorods showed the highest catalytic activity at the temperature below 350 oC due to its more activated molecule. However, smaller particles could lead to deactivation easier at high temperature.Secondly, the effect of Mn-loading on catalytic activity was studied. Mn was loaded on nano-CeO₂ by hydrothermal method, which KMnO4 was added as the precursor. The test results of SEM and TEM showed that CeO₂ was besieged by Mn, resulting in the increasing of particle size, pore diameter, and the specific surface area, which improved the catalytic activity in some extent. As the support, CeO₂ maintain the same during the load experiment. MnOx which loaded on the surface of catalyst, have a well-ordered lamellar and the valence contained +2、+3 and +4. It showed high catalytic activity at low temperature, but easier deactivation at high temperature. Mn-Ce nanorods performed higher activity with the increase of MnOx loading amount on surface.Finally, comparing the experimental results of the catalytic activity of Mn-Ce catalyst, CeO₂ catalyst and MnOx, synergistic reaction mechanism of MnOx and CeO₂ was proposed. According to the results, Mn-Ce catalyst performed the best catalytic activity, in the order as follows: Mn-Ce > Mn Ox > CeO₂, due to their synergetic promotion. The results of TG profiles also provide the synergy evidence between MnOx and CeO₂. The synergistic mechanism of MnOx and CeO₂ over Mn-Ce catalyst could be described as follows. As the active substance, MnOx could promote denitration process by circulation redox itself. As the promotor, CeO₂ could speed up the catalytic reaction by oxidizing MnOx due to its high oxygen storage and adsorbed oxygen conversion capacity.更多还原