负载型铜基纳米复合催化剂的制备及其催化CO氧化性能的研究

发布时间：2018-03-26 14:40

  本文选题：负载型铜基催化剂　切入点：CuO-CeO_2　出处：《山东大学》2017年硕士论文

【摘要】：CO是一种易燃易爆,对人体有害的气体分子污染物。因此必须消除人体周围环境中的CO。目前,人们普遍认为催化氧化技术是消除CO气体污染物的有效方法,由于其高效节能的特点。常用于催化CO氧化反应的催化剂主要有贵金属催化剂和铜基催化剂。贵金属催化剂低温下就具有很高的催化活性,但由于价格昂贵、储量稀少以及稳定性较差等缺点限制了其在实际生产中的应用。而铜基催化剂催化活性虽远不及贵金属催化剂,但其价格低廉、稳定性较好,依然受到人们的关注。CeO_2是一种重要的稀土催化氧化物,具有较强的储放氧能力,因此常被选作催化剂的载体。尤其是在CuO-CeO_2复合催化剂中,铜物种与CeO_2之间较强的协同作用可以有效提高催化剂的催化性能,因此具有较好的应用前景。本论文系统研究了负载型铜基复合催化剂催化CO氧化反应的性能,探究了铜的负载量对CuO-CeO_2纳米片催化剂反应活性的影响,详细指认了催化反应的活性物种。同时还将CuO-CeO_2同时负载在其他功能材料上制备得到三相催化剂,考察其结构与活性之间的关系。并通过一系列表征技术,包括XRD、TEM/HRTEM、Raman、BET、H_2-TPR、XAFS 及in-situ DRIFTS,对催化剂的物相结构和催化性能进行了详细的表征。主要研究内容如下:1.选用二维结构的超薄CeO_2纳米片作为载体,通过沉积沉淀法制备了一系列不同负载量的CuO-CeO_2纳米片催化剂,并对其催化CO氧化性能进行了测试。结果发现5CuCe样品催化活性最好,可能是由于其表面含有较多的CuO活性物种。随着负载量进一步增加到10 wt.%,10CuCe样品表现出了最差的活性,可能是由于表面生成了惰性的体相CuO物种,与XRD及H_2-TPR表征结果一致。根据in-situ DRIFTS测试结果,证明Cu~+物种是CO吸附的活性位点,而它主要来自于表面高分散CuO_x簇的还原。从而表明了表面高分散的CuO_x簇是活性物种,而不是具有强相互作用的Cu-[O_x]-Ce结构,同时体相CuO物种对催化反应的进行有一定的抑制作用。2.选用形貌规则的SiO_2微球作为载体,采用分步法制备了一系列CeO_2包覆量不同和铜负载量不等的Cu-SiO_2@CeO_2复合催化剂,考察了不同CeO_2包覆量和铜负载量对催化性能的影响。结果表明CeO_2包覆量和铜负载量对活性影响较大,其中5Cu-SiO_2@50CeO_2样品性能最好。并对活性最优的5Cu-SiO_2@50CeO_2催化剂进行了 24 h的高温稳定性测试,在温度为600℃、空速为1448,000 mL·gcat~(-1)·h~(-1)的条件下,样品的活性没有任何下降的趋势,稳定性明显优于采用一步共浸渍法制备的5Cu25Ce-SiO_2催化剂。
[Abstract]:Co is a kind of combustible and explosive gas molecular pollutant harmful to human body. Therefore, it is necessary to eliminate CO. at present, it is generally accepted that catalytic oxidation technology is an effective method to eliminate CO gas pollutants. Because of its characteristics of high efficiency and energy saving, the catalysts used to catalyze CO oxidation are mainly noble metal catalysts and copper based catalysts. The noble metal catalysts have high catalytic activity at low temperature, but because of the high price, The shortage of reserves and poor stability limit its application in practical production. Although the catalytic activity of copper based catalyst is far less than that of precious metal catalyst, its price is low and its stability is good. CeOS _ 2 is an important rare earth catalytic oxide with strong oxygen storage and discharge ability, so it is often selected as the support of catalyst, especially in CuO-CeO_2 composite catalyst. The strong synergistic action between copper species and CeO_2 can effectively improve the catalytic performance of the catalyst, so it has a good prospect of application. In this paper, the catalytic performance of supported copper based composite catalyst for CO oxidation was systematically studied. The effect of copper loading on the catalytic activity of CuO-CeO_2 nanoparticles was investigated, and the active species of catalytic reaction were identified in detail. At the same time, three phase catalysts were prepared by loading CuO-CeO_2 on other functional materials at the same time. The relationship between its structure and activity was investigated and characterized by a series of techniques. The phase structure and catalytic performance of the catalyst were characterized in detail, including XRDX / TM / HRTEMN Raman-Bet / H2-TPR-XAFS and in-situ DRIFTS. The main contents of the study are as follows: 1. The ultrathin CeO_2 nanoparticles with two-dimensional structure were selected as the support. A series of CuO-CeO_2 nanocrystalline catalysts with different loading amounts were prepared by deposition precipitation method, and their catalytic activity for CO oxidation was tested. The results showed that 5CuCe samples had the best catalytic activity. It may be that there are more active species of CuO on the surface. As the loading amount increases to 10 wt. the sample of 10CuCe exhibits the worst activity, which may be due to the formation of inert CuO species on the surface. According to the results of in-situ DRIFTS test, it was proved that Cu ~ species are active sites for CO adsorption, and they mainly come from the reduction of highly dispersed CuO_x clusters on the surface, which indicates that the highly dispersed CuO_x clusters on the surface are active species. Instead of Cu- [Ox] -Ce structure with strong interaction, the CuO species in bulk phase have some inhibition on the catalytic reaction. 2. SiO_2 microspheres with regular morphology are selected as the carrier. A series of Cu-SiO_2@CeO_2 composite catalysts with different CeO_2 coating and copper loading were prepared by step method. The effects of different CeO_2 coating and copper loading on the catalytic performance were investigated. The results showed that CeO_2 coating and copper loading had great influence on the catalytic activity. The performance of 5Cu-SiO_2@50CeO_2 sample was the best, and the stability of the 5Cu-SiO_2@50CeO_2 catalyst with the best activity was tested for 24 h. Under the conditions of 600 鈩，

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