负载金属催化剂催化氮氧化物分解研究

发布时间：2018-06-16 06:55

本文选题：氮氧化物 + 直接分解　；参考：《重庆科技学院》2017年硕士论文

【摘要】：氮氧化物(NO_x)是大气主要污染物之一,其过量排放不仅会引起酸雨、光化学烟雾、雾霾等环境问题,严重危害人体健康与生态环境,并且还难以处理。因此,如何高效低成本地脱除工业烟气中的氮氧化物对于防治大气环境污染具有重要意义。在众多氮氧化物脱除方法中,催化脱除法是最具发展前景和经济效益的方法,其中催化剂是该方法的核心。由于工业燃煤锅炉所排放的烟气具有高温、高浓度粉尘和高含量SO_2的特点,易导致催化剂失活,为减少这些因素对催化剂的影响,可将脱硝反应器置于除尘和脱硫装置之后,而此时的烟气温度低于300℃,难以满足传统催化剂V2O5-WO3/TiO_2所需反应温度,若对烟气再次加热到350℃以上,无疑会提高运行成本。因此,研发低温高效的脱硝催化剂是氮氧化物催化脱除方法的关键。本文以硝酸预处理后的活性炭为载体,以Ni、Cu、Mn为活性组分,并辅以稀土氧化铈,采用浸渍法制备了一系列负载型金属氧化物催化剂,用于直接催化分解NO性能研究。考察了载体预处理、浸渍方法等催化剂制备工艺条件,以及烟气条件对催化剂分解活性的影响,并借助BET、FTIR、XRD和TEM表征手段,分析催化剂催化分解NO的反应机理。BET和FTIR结果表明,HNO3预处理活性炭,不仅可增大其比表面积和孔容,还可以改变官能团的种类与数量,以及减少活性炭表面的杂质成分。在直接催化分解NO反应体系中,三种不同金属氧化物的活性顺序为NiOCuOMnO_2,CeO_2的改性可进一步提高NiO/AC的活性,其中Ce4+/Ce3+和Ni2+/Ni3+具有强氧化还原能力,能加快还原/氧化循环,从而可提高NO转化率。XRD和TEM表征结果显示,采用共同浸渍法形成的NiO和CeO_2结晶度低,晶粒小且均匀分散在活性炭表面上,当Ni O和CeO_2负载量分别为5%和3%时,该催化剂活性最佳,当温度为300℃时,NO浓度在200~600ppm之间,空速在3900~5850h-1之间,氧含量在1~8%之间,其NO转化率可保持在90~99%范围内,该催化剂用于直接催化分解NO,操作弹性大,抗氧性能强,脱硝率高,且该工艺无需NH3等有毒易燃易爆气体作为还原剂,可避免二次污染,降低脱硝过程中的危险性。本文研究了催化剂MO_x/AC和MO_x-CeO_2/AC的低温SCR性能,结果表明三种不同金属氧化物的低温SCR活性顺序为:MnO_2CuONiO,该活性顺序与直接催化分解NO的活性顺序正好相反,进一步证明了催化剂具有选择性,在低温SCR反应体系中,MnO_2具有较好的低温SCR活性。XPS表明,MnO_2-CeO_2/AC中的Mn元素主要以Mn4+形式存在,而Ce元素主要以Ce4+和Ce3+共存,可增强电子之间的转移,有利于活性位再生,使得MnO_2-CeO_2/AC表现出较好的低温SCR活性。当MnO_2与CeO_2负载量分别为5%和3%时,该催化剂活性最佳,当反应温度为75℃,n(NH3/NO)=1,空速在3900~9749h-1范围内,氧含量在3~7%范围内时,其NO转化率可维持在90~99%左右,该催化剂适用于除尘脱硫工艺后,无需再次加热,可有效降低运行成本,且所需反应温度低至75℃,可避免高温SCR反应器和蒸汽对人体的高温危害。
[Abstract]:Nitrogen oxide (NO_x) is one of the main pollutants in the atmosphere. Its excessive emission not only causes environmental problems such as acid rain, photochemical smog and fog haze, but also seriously endangering human health and ecological environment, and it is difficult to deal with. Therefore, it is important to remove nitrogen oxides from industrial flue gas to prevent and control atmospheric pollution. In many nitrogen oxides removal methods, catalytic removal is the most promising and economic benefit method. The catalyst is the core of the method. Because the flue gas emitted by the industrial coal-fired boiler has the characteristics of high temperature, high concentration of dust and high content of SO_2, it is easy to cause the deactivation of the catalyst, in order to reduce the effect of these factors on the catalyst. The denitrification reactor can be placed after the dedusting and desulphurization device, and the temperature of the flue gas is below 300 C at this time, and it is difficult to meet the reaction temperature of the traditional catalyst V2O5-WO3/TiO_2. If the flue gas is reheated to more than 350 C, it will undoubtedly increase the operating cost. Therefore, the research and development of the low temperature and high efficiency denitrification catalyst is the catalytic removal of nitrogen oxides. The key of the method. In this paper, a series of supported metal oxide catalysts were prepared by impregnation method with active carbon as the carrier, Ni, Cu, Mn as active components and rare earth cerium oxide, and used to prepare a series of supported metal oxide catalysts for direct catalytic decomposition of NO. The effect of gas conditions on the decomposition activity of the catalyst, and by means of BET, FTIR, XRD and TEM, analysis of the reaction mechanism of catalytic decomposition of NO by catalyst.BET and FTIR results show that HNO3 pretreated activated carbon can not only increase the specific surface area and Kong Rong, but also change the species and quantity of functional groups, and reduce the impurity components on the surface of activated carbon. In the direct catalytic decomposition NO reaction system, the activity sequence of three different metal oxides is NiOCuOMnO_2. The modification of CeO_2 can further improve the activity of NiO/AC, of which Ce4+/Ce3+ and Ni2+/Ni3+ have strong oxidation-reduction ability and can accelerate the reduction / oxidation cycle. Thus, the NO conversion rate.XRD and TEM characterization results can be shown to be used in common immersion. The crystallinity of NiO and CeO_2 formed by the method is low, and the grain is small and evenly dispersed on the surface of activated carbon. When the load of Ni O and CeO_2 are 5% and 3% respectively, the activity of the catalyst is the best. When the temperature is 300, the NO concentration is between 200~600ppm, the velocity of space is 3900~5850h-1, the oxygen content is between 1~8%, and the NO conversion can be kept in the 90~99% range. The catalyst is used to catalyze the decomposition of NO directly, with high elasticity, strong oxygen resistance and high denitrification rate, and the process does not need NH3 and other flammable and explosive gases as reducing agent. It can avoid two pollution and reduce the danger in the process of denitrification. This paper studied the SCR properties of the catalyst MO_x/AC and MO_x-CeO_2/AC at low temperature. The results showed that three kinds of gold were different. The order of SCR activity at low temperature of the genus oxide is MnO_2CuONiO, which is the opposite of the order of activity that directly catalyzes the decomposition of NO. It further proves that the catalyst is selective. In the low temperature SCR reaction system, MnO_2 has a good low temperature SCR active.XPS, which indicates that the Mn element in MnO_2-CeO_2/AC is mainly in Mn4+, and the Ce element is in the Ce element. The coexistence of Ce4+ and Ce3+ can enhance the transfer of electrons and benefit the regeneration of active sites, which makes MnO_2-CeO_2/AC exhibit good low temperature SCR activity. When the load of MnO_2 and CeO_2 is 5% and 3%, the catalyst has the best activity, when the reaction temperature is 75, n (NH3/ NO) =1, the air velocity is within the 3900~9749h-1 range, and the oxygen content is in 3~7% range. At the time, the conversion rate of NO can be maintained at about 90~99%. The catalyst is suitable for the dedusting and desulphurization process. It can not be reheated again, and it can effectively reduce the operating cost, and the required reaction temperature is low to 75 C, which can avoid the high temperature damage to the human body by the high temperature SCR reactor and steam.
【学位授予单位】：重庆科技学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X701

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