【作者】 姜建清；

【导师】 施耀；

【作者基本信息】 浙江大学 ， 环境科学， 2012， 硕士

【摘要】 选择性催化还原法(SCR)是机动车贫燃尾气氮氧化物(NOx)控制的主要方法,分子筛催化剂是一类颇具应用前景的SCR催化剂。本文选用H-BEA分子筛为载体,过渡金属元素Ni为主要活性组分,并以Fe为助剂,采用浸渍法制备了一系列Ni/H-BEA和Ni-Fe/H-BEA催化剂,并以NH3、CH4、C3H8等为还原剂,对Ni/H-BEA和Ni-Fe/H-BEA催化剂上NH3-SCR、HC-SCR以及低温等离子体协同HC-SCR三种过程脱除贫燃尾气NOx进行了深入研究,得到了以下一些结论：(1)在NH3-SCR体系,3%Ni/H-BEA的活性最高,最佳活性温度范围为350-500℃,NOx转化率最高可达100%。在较高空速范围内(20000～100000 h-1),Ni/H-BEA的活性随空速的增加而下降。催化剂的活性随着NH3/NO摩尔比的上升而上升,较适宜的NH3/NO比为1。在一定的O2浓度范围内(4-10%),Ni/H-BEA的活性受O2浓度的变化影响较小。SO2和H2O在300℃下对催化剂活性有不可逆的抑制作用,NOx转化率最高降幅可达20%,主要是因为铵盐在催化剂表面的形成。(2)在HC-SCR体系,Ni/H-BEA的C3H8-SCR活性远高于其CH4-SCR活性。Fe掺杂的Ni-Fe/H-BEA催化剂具有很好的低温活性,其中3%Ni-1%Fe/H-BEA的C3H8-SCR活性最高。Ni-Fe/H-BEA催化剂上的活性组分以NiO和a-Fe2O3为主,Fe的掺杂提高了催化剂活性组分的分散度和酸性。O2在C3H8-SCR反应中扮演重要角色。在300℃下,1000 ppm之内的NO浓度水平对催化剂活性没有明显影响,在其他考察温度下,随着NO浓度增高,NOx去除率下降。随着C3H8/NO升高,在所有考察温度下NOx转化率也逐渐上升。在300℃时,C3H8/NO=1.25时,NOx转化率达到了100%。此外,Fe掺杂极大地改善了Ni-Fe/H-BEA催化剂的抗水抗硫性。(3)引入DBD低温等离子与C3H8-SCR的结合,在低温下具有明显的协同效应,在250℃和275℃时协同因子为1.07；此外,NTP的引入有效地提高了催化剂的抗水抗硫性。更多还原

【Abstract】 Selective catalytic reduction (SCR) will be the mainstay for nitrogen oxides (NOx) removal from lean-burn conditions, and zeolite-based catalysts are considered to be SCR catalysts with prospective. In this work, we developed a series of Ni/H-BEA and Ni-Fe/H-BEA catalysts by impregnation. Then the catalytic activities of these catalysts for NH3-SCR, HC-SCR, and NTP-assisted C3H8-SCR processes were carried out under a lean-burn condition. The main conclusions are as follows:In the NH3-SCR system, the 3%Ni/H-BEA showed the highest activity among all samples, its optimum reaction temperature range from 350 to 500℃. The activity of Ni/H-BEA declined as the GHSV increased from 20000 to 100000 h"1. NOx conversion increased as the NH3/NO molar ratio increased, the most suitable NH3/NO molar ratio was 1. The effect of oxygen concentration (4-10%) on catalytic activity of Ni/H-BEA was insignificant. The activity of Ni/H-BEA was inhibited in the presence of SO2 and H2O, mainly due to the ammonium salts formed on the catalyst.In the HC-SCR system, the C3H8-SCR activity was higher than the CH4-SCR activity over Ni/H-BEA. The addition of iron significantly lowered the optimum reaction temperature of Ni/H-BEA. The 3%Ni-1%Fe/H-BEA had the highest activity among samples with different bimetal loadings. The main active components over Ni-Fe/H-BEA were NiO andα-Fe203. The addition of iron increased the nickel dispersion on the surface of catalyst and the acidity as well. Oxygen played an important role in activating NO and propane during the C3H8-SCR reaction. The NOx conversions decreased as the initial NO concentration increased at all investigated temperatures except 300℃. NOx conversion increased as the C3H8/NO molar ratio increased, a complete conversion of NOx was achieved with C3H8/NO=1.25 at 300℃. The addition of iron to Ni/H-BEA notably improved the tolerance of SO2 and H2O.The synergetic effect between NTP and C3H8-SCR was obvious at low temperature, the inhibition of SO2/H2O was eliminated by the introduction of NTP.更多还原