掺杂型Pd基催化剂的制备及三效催化性能研究

发布时间：2018-05-19 17:58

本文选题：掺杂型Pd催化剂 + 负载型Pd催化剂　；参考：《北京工业大学》2015年硕士论文

【摘要】：三效催化剂是控制汽车尾气排放污染物的有效手段,贵金属Pt、Rh和Pd是其活性组分。随着汽车保有量的逐年增加,贵金属需求量越来越大,导致其价格不断攀升。同时,即将实施的国V汽车排放标准要求尾气排放达标里程数从10万公里增加到了16万公里,催化剂需要具有更好的耐久性。因此,在保证催化剂三效催化活性的前提下,如何减少贵金属用量和提高三效催化剂的高温热稳定性和耐久性是目前三效催化剂产业面临的难题。本论文针对以上两个难题,在前期研究基础之上,制备了不同结构的贵金属掺杂型Pd基催化剂,采用SEM、TEM、XRD、H2-TPR、UV-Raman、XPS等多种技术对所得催化剂的物化性能进行了表征,评价了其三效催化活性,并对其热稳定性进行了研究。主要研究内容和结果如下:(1)采用胶体晶体模板法制备了系列不同Pd含量的三维有序大孔(3DOM)Ce0.7-xZr0.3PdxO2(x=0,0.01,0.02,0.05,0.07,0.1)催化剂,所得样品具有规整的三维有序大孔结构。Pd的掺杂量存在一个阈值,当x≤0.05时,样品为立方萤石结构,没有检测到Pd物种的存在,然而当x≥0.07时,则检测到痕量的PdO。当x=0.05时,样品表现出最佳的低温还原性能和三效催化活性,CO、HC和NO在3DOM Ce0.65Zr0.3Pd0.05O2上的完全转化温度(T90)分别为153、223和216°C,其活性和3DOM Ce0.6Zr0.3Pd0.1O2的三效催化活性相当。(2)为了考察掺杂型催化剂3DOM Ce0.65Zr0.3Pd0.05O2的热稳定性,采用浸渍法制备了Pd含量相同的负载型催化剂3.42 wt%Pd/3DOM Ce0.7Zr0.3O2作为对比催化剂,对两种不同类型的Pd基催化剂的三效催化活性及水热稳定性进行了对比研究。结果表明,无论掺杂型还是负载型催化剂,Pd的引入都未破坏规整的三维有序大孔结构。无论是新鲜样品还是老化样品,负载型Pd基催化剂具有更好的三效催化活性,但是对HC和NO转化,掺杂型Pd基催化剂老化前后的?T50和?T90均小于负载型Pd基催化剂,即掺杂型Pd基催化剂具有更好的高温热稳定性,这是由于Pd物种进入CeO2晶格形成-Pd-O-Ce-链接,抑制了Pd物种的自由迁移所致。(3)为了考察孔结构对三效催化活性的影响,分别采用软硬双模板法、胶体晶体模板法和溶胶凝胶法制备了具有介孔孔壁的三维有序大孔3DOM-meso Ce0.65Zr0.3Pd0.05O2、3DOM Ce0.65Zr0.3Pd0.05O2和无孔Ce0.65Zr0.3Pd0.05O2催化剂,并对它们的物化性能、三效催化活性和热稳定性进行了对比研究。结果表明3DOM-meso Ce0.65Zr0.3Pd0.05O2催化剂具有最佳的三效催化活性和高温热稳定性,CO、HC和NO在220°C之前可以完全转化,老化后CO和NO的完全转化温度仅仅提高了40°C左右。(4)为了进一步提高掺杂型Pd基催化剂的三效催化活性,又调整了铈锆比,采用溶胶凝胶法制备了系列纳米Ce0.5-x/2Zr0.5-x/2PdxO2,并对Pd的最佳掺杂量进行了研究。结果表明,所得样品为粒径约10 nm的纳米粒子。Pd的掺杂量和三效催化活性之间不存在线性关系,其中,对于x=0.01的样品,其三效催化活性和x=0.08的样品的活性相当,对CO、HC和NO的T90分别为156、223和196°C,然而,Ce0.495Zr0.495Pd0.01O2中贵金属Pd的用量仅为Ce0.46Zr0.46Pd0.08O2样品中Pd含量的20%,大大降低了贵金属用量,为贵金属减量提供了数据支持。
[Abstract]:The three effect catalyst is an effective means to control the exhaust emission of automobile exhaust. The Pt, Rh and Pd of precious metals are its active components. With the increasing of the car's insured quantity, the demand for precious metals is increasing, which leads to the rising price. At the same time, the emission standard of the national V vehicle that will be implemented is required to increase the mileage of the tail gas from 100 thousand kilometers. At 160 thousand km, the catalyst needs better durability. Therefore, how to reduce the amount of precious metals and improve the thermal stability and durability of the three effect catalyst is a difficult problem for the three effect catalyst industry on the premise of ensuring the catalytic activity of the catalyst in the three effect. This paper is based on the above two difficult problems in the previous research basis. On the other hand, the Pd based catalysts with different structures were prepared. The physical and chemical properties of the catalysts were characterized by SEM, TEM, XRD, H2-TPR, UV-Raman, XPS and so on. The three effect catalytic activity was evaluated and their thermal stability was studied. The main contents and results are as follows: (1) the colloidal crystal template method is used. A series of three dimensional ordered macroporous (3DOM) Ce0.7-xZr0.3PdxO2 (x=0,0.01,0.02,0.05,0.07,0.1) catalysts with different Pd content are prepared. The sample has a regular three-dimensional ordered macroporous structure.Pd doped with a threshold. When x < 0.05, the sample is a cubic fluorite structure, and the existence of Pd species is not detected. However, when x is more than 0.07, then the number of Pd species is not detected. When the trace PdO. was detected as x=0.05, the sample showed the best low temperature reduction and three effect catalytic activity. The total conversion temperature (T90) of CO, HC and NO on 3DOM Ce0.65Zr0.3Pd0.05O2 was 153223 and 216 degrees C, respectively, and the activity of the 3DOM Ce0.6Zr0.3Pd0.1O2 was equal to that of the 3DOM Ce0.6Zr0.3Pd0.1O2. (2) in order to investigate the doped catalyst 3DOM The thermal stability of 0.3Pd0.05O2 was made by impregnation, and 3.42 wt%Pd/3DOM Ce0.7Zr0.3O2 with the same Pd content was prepared as the contrast catalyst. The three effect catalytic activity and the hydrothermal stability of the two different types of Pd based catalysts were compared. The results showed that the doping type or the load type catalyst and the introduction of Pd were introduced. None of the regular three-dimensional ordered macroporous structures. Both fresh and aging samples, the supported Pd based catalysts have better three catalytic activity. But for the conversion of HC and NO, the T50 and T90 of the doped Pd based catalysts are less than those of the loaded Pd based catalysts, that is, the doping type Pd based catalysts have better heat heat. Stability, which is due to the Pd species entering the CeO2 lattice to form the -Pd-O-Ce- link and inhibit the free migration of the Pd species. (3) in order to investigate the effect of the pore structure on the three effective catalytic activity, the soft and hard double die plate method, the colloidal crystal template method and the sol-gel method were used to prepare the three-dimensional ordered macroporous 3DOM-meso Ce0.65Zr0 with the mesoporous pore wall. .3Pd0.05O2,3DOM Ce0.65Zr0.3Pd0.05O2 and non porous Ce0.65Zr0.3Pd0.05O2 catalysts were used to compare their physical and chemical properties, three effect catalytic activity and thermal stability. The results show that 3DOM-meso Ce0.65Zr0.3Pd0.05O2 catalyst has the best three effect catalytic activity and high temperature thermal stability. CO, HC and NO can be complete before 220 degrees C. After aging, the complete conversion temperature of CO and NO was only about 40 C. (4) in order to further improve the three effect catalytic activity of the doped Pd based catalyst and adjust the ratio of cerium to zirconium, a series of nano Ce0.5-x/2Zr0.5-x/2PdxO2 was prepared by sol-gel method, and the best doping amount of Pd was studied. The results showed that the sample was obtained. There is no linear relationship between the doping amount and the three effect catalytic activity of nanoparticles with a particle size of about 10 nm, and for the samples of x=0.01, the activity of the three effect catalytic activity is equal to the activity of the sample of x=0.08, and the T90 of CO, HC and NO is 156223 and 196 degrees C respectively. However, the Pd amount of noble metals in Ce0.495Zr0.495Pd0.01O2 is only Ce0.46Zr0.46Pd0.08O. 2 the Pd content of the sample is 20%, which greatly reduces the amount of precious metals and provides data support for the reduction of precious metals.
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;X734.2

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