Pt基催化剂用于NO催化还原性能研究

发布时间：2018-06-16 10:27

  本文选题：NO + 低温催化还原　； 参考：《浙江工业大学》2015年硕士论文

【摘要】：氮氧化物(nitrogen oxides)是大气污染物中主要的有害成分,主要包含NO,NO2,N2O等,它们是造成光化学烟雾和酸雨的一个重要原因。降解氮氧化物有许多行之有效的方法,其中催化还原技术是现阶段发展较为成熟的方法之一,而又以NH3-SCR法最先开始工业化。但是NH3是一种危害性气体,在使用中易造成安全事故,对设备要求较高,而且无法应用到移动源的氮氧化物处理中。因此H2-SCR逐渐开始走入人们视线,且贵金属催化剂在低温情况下展现了较好的催化还原能力。我们课题组制备的组合型Pt催化剂其制备过程简单,可重复性高,有其独特的方法优势:(1)Pt前驱体在高压H2环境中还原,能充分地还原Pt。(2)碳酸丙二醇酯(PC)作为分散剂兼稳定剂,无毒无害,性质稳定,得到的Pt纳米溶液能长时间保持稳定状态。(3)高分散的Pt纳米颗粒再吸附到载体避免了直击浸渍法搅拌不均匀的缺陷,使得活性组分分散性更高。(4)直接吸附法全过程无氯。通过该法制备得到的催化剂在邻氯硝基苯加氢反应、VOCs催化氧化方面已经证实了有非常好的催化效果,并且贵金属催化剂对H2-SCR反应有很好的低温催化效果,因此将该方法制备的Pt基催化剂用于H2-SCR反应,探究其在还原NO方面的催化特性,并讨论了催化性能与催化剂结构性质的内在联系。论文主要按照以下几个方面展开:一、Pt/Ti O2催化剂催化还原NO性能研究以Ti O2为载体,采用直接吸附法将制备得到的Pt纳米颗粒吸附到Ti O2载体上,从而制备出Pt/Ti O2催化剂(Pt/Ti O2-AS),并以NO还原反应为探针反应,研究其催化效果。结果表明:组合型Pt/Ti O2催化剂在6%O2体积分数、H2/NO摩尔比为7、空速为120000 ml·g-1·h-1时具有较高的NO转化率,在低温70℃时转化率最高能达到80%,且在50-220℃的范围内都能保持较高活性。同样制备条件下,其他载体和其他活性组分未能表现出更高活性。为探讨载体酸碱性对反应的影响,通过添加K2SO4、KOH等助剂来改变催化剂表面的酸性位。实验证明,保持催化剂上的酸性位更有利于NO还原反应,而添加碱性助剂不利于该反应。二、Pt/Si O2催化剂上催化还原NO性能研究Si O2具有极大的比表面积,更有利于活性组分的分布,且酸性载体更利于NO还原反应,因此选用Si O2作为载体,对比了直接吸附法和传统浸渍法制备得到的催化剂在H2-SCR反应的催化能力,进而得出直接吸附法的优势所在。结果表明:Si O2载体在温度低至58℃时转化率就能达到80%,展现了较高的低温催化活性。结合各种表征结果得出Pt/Si O2-AS催化剂表面上Pt更多以Pt0形式存在,并且碳酸丙二醇酯(PC)作为分散剂,使制得的Pt纳米颗粒均一稳定,Pt物种主要以还原态的Pt均匀稳定地分散在载体表面,能更好地与反应物接触,显示出良好的低温催化能力。
[Abstract]:Nitrogen oxides are the main harmful components of atmospheric pollutants, including no _ (no _ 2) _ (2) N _ (2) O and so on. They are an important cause of photochemical smog and acid rain. There are many effective methods for the degradation of nitrogen oxides, among which catalytic reduction is one of the more mature methods at present, and the NH _ 3-SCR method is the first to begin industrialization. However, NH _ 3 is a dangerous gas, which can easily cause safety accidents in use, require high equipment, and can not be applied to the nitrogen oxide treatment of moving sources. Therefore, H2-SCR gradually began to be seen, and the noble metal catalyst showed good catalytic reduction ability at low temperature. The composite Pt catalyst prepared by our group has the advantages of simple preparation process and high repeatability. It has its unique advantages in reducing the Pt precursor in high pressure H 2 environment, and can fully reduce Pt.2) propanediol carbonate (PC) as both dispersant and stabilizer. The Pt nanoparticles with high dispersion can be adsorbed to the carrier for a long time to avoid the defect of non-uniform stirring by direct impact impregnation. The dispersivity of the active component is higher. 4) the whole process of direct adsorption is chlorine free. The catalyst prepared by this method has been proved to have a very good catalytic effect in the catalytic oxidation of o-chloronitrobenzene in the presence of VOCs, and the noble metal catalyst has a good catalytic effect at low temperature for the H2-SCR reaction. Therefore, the Pt-based catalyst prepared by this method was used in the H2-SCR reaction to investigate its catalytic properties in the reduction of no, and the intrinsic relationship between the catalytic performance and the structural properties of the catalyst was discussed. The main contents are as follows: firstly, the catalytic reduction of no on Pt / TIO _ 2 catalyst was studied. The Pt nanoparticles were adsorbed on TIO _ 2 carrier by direct adsorption method. The catalytic effect of Pt / TIO _ 2 catalyst was studied by using no reduction reaction as probe reaction. The results show that the combined PTT / TIO _ 2 catalyst has a high no conversion when the molar ratio of H _ 2 / no is 7 and the space velocity is 120000 ml g ~ (-1) h ~ (-1). The highest conversion of no can be reached at 70 鈩，

本文编号：2026347