用于氨气选择性催化还原氮氧化物组合催化剂的研究

发布时间：2018-10-11 14:15

【摘要】：随着我国工业的发展以及汽车使用量的增长,大量的煤炭和石油被燃烧使用,燃烧后产生的尾气对地球的大气产生了严重的污染。随之而来的一系列的如酸雨,雾霾,全球气候变暖等大气污染问题对我国人民的生活以及整个人类社会的发展产生了巨大的影响。可以说大气的污染威胁着我们的身体健康和生活环境。氮氧化物(NOx)就是大气污染物中的主要一种,主要包括NO和NO2以及少量的N2O。我国对氮氧化物的排放也变得很严格。氨气选择性催化还原氮氧化物法(NH3-SCR)是一种成熟可靠、效率高、选择性好并且具有良好的性价比的脱硝方法。虽然V-W(Mo)/TiO2催化剂在火电厂上已经得到了成熟的应用,但是钒系催化剂仍然存在着操作温度较高、操作温度窗口较窄、高温时N2选择性下降,以及SO2向SO3氧化等问题。因此,效果良好的新型NH3-SCR催化剂的开发仍然是我们应该努力的方向。本文第三章制备了几种氧化性不同的单一金属氧化物。通过不同氧化性的单一金属氧化物活性的对比,发现金属氧化物催化剂的氧化性对于NH3-SCR具有重要作用。氧化性较好的金属氧化物催化剂往往在低温下具有良好NH3-SCR催化反应活性,但是在反应的时候会生成大量的NO2和N2O造成其N2选择性较差。选择氧化性强低温活性好的MnOx来进行改性,其中沉淀法合成的MnOx主要为Mn5O8,而通过水热合成法合成的MnOx主要为MnO2。水热法合成的MnOx虽然较沉淀法合成的MnOx活性有了进一步提高,但是其反应的选择性依然较差。通过对沉淀法合成的MnOx进行硫酸处理制备了SO42-/MnOx催化剂,大大地提高了反应的选择性与活性。通过一系列的表征发现SO42-的引入对MnOx起到了钝化催化剂的作用,在降低MnOx氧化性的同时还提高了MnOx表面氧的量从而提高了 MnOx的催化活性。本文第四章制备了一系列酸性不同的金属氧化物。通过对这些酸性不同的金属氧化物催化剂进行NH3-SCR活性评价,发现金属氧化物的酸性对于反应具有重要的作用。酸性较强的金属氧化物往往具有较好的高温活性,而且其N2选择性较高。选择Fe2O3对其进行酸处理制备了SO42-/Fe2O3超强酸催化剂。硫酸处理后的SO42-/Fe2O3催化剂在活性与选择性上也有了很大的提高,并进行一系列的表征来对SO42-/Fe2O3催化剂进行分析,发现SO42-的引入在提高Fe203的酸性的同时也提高了催化剂表面活性氧的含量从而提高了其反应的活性。本文第五章选择了在低温下具有优势的一系列的Mn系复合金属氧化物与高温活性较好的Ce系复合金属氧化物。通过对这两个系列的复合金属氧化物进行活性评价发现,Mn系的复合金属氧化物虽然在低温的时候具有较好的NO转化率。但是,在反应过程中会生产大量的副产物从而降低了反应的N2选择性。Ce系复合金属氧化物催化剂具有较好的高温活性和N2选择性。进一步选择了MnFeOx复合金属氧化物对其进行酸化处理制备了SO42-/MnFeOx催化剂。SO42-/MnFeOx虽然在低温活性上有所下将,但是在较高温度的活性与选择性却有了很大的提升。本文第六章选择了几种前期制备的单一金属氧化物、复合金属氧化物、改性后的单一金属氧化物。然后通过三种不同的组合方式制备出组合催化剂并对其进行NH3-SCR活性评价。经过实验发现在对催化剂进行组合时,往往是将酸性较好的高温活化剂放置在前半段,将氧化性较好的低温催化剂放放置在后半段而组合成的催化剂具有最好的催化活性与选择性。
[Abstract]:With the development of China's industry and the growth of automobile usage, a great deal of coal and oil are used for combustion, and the tail gas produced after combustion produces serious pollution to the earth's atmosphere. The ensuing series of air pollution problems, such as acid rain, haze and global warming, have a great impact on our people's lives and the development of the whole human society. It can be said that the pollution of the atmosphere threatens our health and living environment. Nitrogen oxides (NOx) are one of the main pollutants in atmospheric pollutants, mainly including NO and NO2 and a small amount of N2O. Our country's emission of nitrogen oxides has also become very strict. Ammonia-selective catalytic reduction of nitrogen oxide (NH3-SCR) is a kind of denitration method with reliable, high efficiency, good selectivity and good cost performance. Although the V-W (Mo)/ TiO2 catalyst has been applied in thermal power plant, it still has the problems of high operating temperature, narrow operating temperature window, selective decrease of N2 at high temperature, oxidation of SO2 to SO3, etc. Therefore, the development of a novel NH3-SCR catalyst with good effect is still the direction we should strive for. In the third chapter, several kinds of single metal oxides with different oxidizability are prepared. It is found that the oxidation of metal oxide catalysts plays an important role in NH3-SCR by comparison of the activity of a single metal oxide with different oxidation properties. The oxidation-resistant metal oxide catalysts tend to have good NH3-SCR catalytic reaction activity at low temperatures, but a large number of NO2 and N2O are generated during the reaction resulting in poor N2 selectivity. The MnOx synthesized by the precipitation method is Mn5O8, and MnOx synthesized by hydrothermal synthesis is mainly MnO2. The MnOx synthesized by hydrothermal method has further improved MnOx activity, but its selectivity is still poor. Through the sulfuric acid treatment of the MnOx synthesized by the precipitation method, the SO42-/ MnOx catalyst is prepared, and the selectivity and the activity of the reaction are greatly improved. By means of a series of characterization, it has been found that the introduction to MnOx plays a role in passivating the catalyst, while reducing MnOx oxidation, increasing the amount of oxygen on the surface of MnOx so as to improve the catalytic activity of MnOx. In the fourth chapter, a series of acid different metal oxides are prepared. Through the NH3-SCR catalytic activity evaluation of these acidic metal oxide catalysts, it was found that the acidity of metal oxides plays an important role in the reaction. Metal oxides with stronger acidity tend to have better high temperature activity, and their N2 selectivity is higher. Fe _ 2O _ 3 superacid catalyst was prepared by acid treatment of Fe2O3. After the sulfuric acid treatment, the Fe-/ Fe 2O 3 catalyst is greatly improved in activity and selectivity, and a series of characterization is carried out to analyze the SO42-/ Fe2O3 catalyst, It has been found that the introduction of hydrogen peroxide in the improvement of the acidity of Fe203 also increases the content of active oxygen species on the surface of the catalyst, thereby increasing the activity of its reaction. In the fifth chapter, a series of Mn-based composite metal oxides with good high-temperature activity are selected at low temperature. Through the active evaluation of the composite metal oxides of these two series, the composite metal oxide of Mn series has better NO conversion rate at low temperature. However, a large number of by-products are produced during the reaction, thereby reducing the N2 selectivity of the reaction. The Ce series composite metal oxide catalyst has better high temperature activity and N2 selectivity. The MnFeOx composite metal oxide is further selected to acidify it to prepare the Ni-/ MnFeOx catalyst. Although Fe-/ MnFeOx has been reduced at low temperature activity, the activity and selectivity at higher temperatures are greatly improved. In Chapter 6, we select a single metal oxide, composite metal oxide and modified single metal oxide. The combined catalyst was then prepared by three different combinations and the NH3-SCR activity was evaluated. Experiments show that when the catalyst is combined, the high-temperature active agent with good acidity is often placed in the front half section, and the catalyst which is formed by placing the low-temperature catalyst with good oxidation resistance in the second half section has the best catalytic activity and selectivity.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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