镍基和镍钴双金属催化剂用于乙醇重整制氢反应的研究

发布时间：2018-01-27 17:05

本文关键词： 乙醇制氢钙钛矿复合氧化物合金积碳烧结　出处：《天津大学》2016年博士论文　论文类型：学位论文

【摘要】：目前,文献报道的乙醇水蒸气重整制氢(SRE)催化剂普遍具有良好的反应活性和氢气选择性,因此近几年来的研究热点以及亟需解决的核心问题是如何提高催化剂的稳定性以及降低催化剂成本。本论文选用了过渡金属Ni和Co作为催化剂的活性组分,它们有着成本低的天然优势。在SRE反应中,低温下催化剂表面的碳沉积和高温下活性组分的烧结是导致催化剂失活的主要原因。针对这两种问题,本论文提出了三种设计思路以期提高催化剂的稳定性:1、向催化剂中添加碱性助剂;2、将催化剂制备成负载型双金属合金催化剂;3、制备高比表面的载体进行活性组分的担载,考察催化剂的孔道结构与其性能之间的联系。首先,通过柠檬酸一步络合的方法制备不同含量钾掺杂的钙钛矿型复合金属氧化物La_(1-x)K_xFe_(0.7)Ni_(0.3)O_3(x=0,0.05,0.1)催化剂前驱体。将还原后的催化剂用于乙醇水蒸气重整制氢反应表现出很好的活性和氢气选择性,尤其是还原后的La_(0.9)K_(0.1)Fe_(0.7)Ni_(0.3)O_3催化剂在反应温度为650°C,水醇比为3:1和空速为264000mL?gcat-1?h-1的条件下反应30小时没有出现明显失活。与不掺杂K的催化剂相比,掺杂K的催化剂有着更好的稳定性,其原因是K的给电子作用提高了Ni表面的电子云,当C2产物在催化剂表面金属镍活性位点上吸附时,C-Ni键增强而C-C键减弱,从而促进C-C键的断裂。催化剂抗积碳性能增强,提高了稳定性。其次,以LaCo_xNi_(1-x)O_3/ZrO_2(x=0,0.3,1)为前驱体用于SRE反应。LaCo_xNi_(1-x)O_3中钴离子和镍离子的还原性质相近,能在同一个还原峰内同时从钙钛矿结构中还原成金属态,因此期望用此种方法制备出ZrO_2载体上担载的Ni、Co和Ni-Co合金催化剂。这组催化剂在SRE反应中表现出很好的活性和稳定性。XRD、TPR和TEM等结果均表明还原后的LaCo_(0.3)Ni_(0.7)O_3/ZrO_2形成了Ni-Co合金颗粒分散在氧化镧修饰的ZrO_2载体上的结构。双金属催化剂由于Ni和Co的协同作用,在SRE反应中有着最好的催化表现,包括高活性、高氢气选择性及良好的稳定性。这种设计思路在催化领域有着广泛的应用,这是因为载体的种类是可调变的,同时钙钛矿中A、B位的金属离子也是可调变的。最后,通过柠檬酸一步络合法和PS模板法分别制备了Ce_(0.5)Zr_(0.5)O_2和大孔Ce_(1-x)Zr_xO_2(x=0,0.5)作为载体。将氧化镍负载在不同孔结构的载体上作为催化剂前驱体用于乙醇重整制氢反应。大孔Ce_(0.5)Zr_(0.5)O_2负载的镍催化剂在反应中有着最好的催化表现,与其他两个催化剂相比,活性和稳定性最好。
[Abstract]:At present, the reported SRE catalysts for hydrogen production from ethanol steam reforming generally have good reaction activity and hydrogen selectivity. Therefore, in recent years, the research focus and the core problem to be solved is how to improve the stability of the catalyst and reduce the catalyst cost. In this paper, the transition metals Ni and Co are selected as the active components of the catalyst. They have the natural advantage of low cost. In SRE reaction, carbon deposition on the catalyst surface at low temperature and sintering of active components at high temperature are the main reasons leading to the deactivation of the catalyst. In this paper, three kinds of design ideas are proposed to improve the stability of the catalyst: 1 and to add alkaline additives to the catalyst. (2) the catalyst is prepared into a supported bimetallic alloy catalyst; 3. The support with high specific surface was prepared to support the active component, and the relationship between the pore structure and the performance of the catalyst was investigated. Potassium doped perovskite-type composite metal oxide (La_(1-x)K_xFe_(0.7)Ni_(0.3)O_3(x=0) was prepared by citric acid one-step complexation method. The catalyst precursor showed good activity and hydrogen selectivity when the reduced catalyst was used in the steam reforming of ethanol to produce hydrogen. Especially, the reduced La_(0.9)K_(0.1)Fe_(0.7)Ni_(0.3)O_3 catalyst was prepared at 650 掳C. The ratio of water to alcohol is 3: 1 and the space velocity is 264000mL? Gcat-1? Under the condition of h-1, there was no obvious deactivation at 30 hours. Compared with the catalyst without doping K, the catalyst doped with K had better stability. The reason is that the electron cloud on Ni surface is enhanced by the electron transfer of K. When C2 product is adsorbed on the active site of nickel on the catalyst surface, the C-Ni bond increases and the C-C bond weakens. Thus, the fracture of C-C bond is promoted. The resistance to carbon deposition of the catalyst is enhanced, and the stability is improved. Secondly, the LaCoxNitix _ (1-x) / O _ (3 / ZrO _ (2)) / x _ (0) 0. 3 is used to improve the stability of the catalyst. 1) the reduction properties of cobalt ion and nickel ion in SRE reaction. It can be reduced to metal state from perovskite structure at the same time in the same reduction peak, so it is expected that Ni supported on ZrO_2 carrier can be prepared by this method. Co and Ni-Co alloy catalysts. This group of catalysts showed good activity and stability in SRE reaction. The results of TPR and TEM show that the reduced LaCoS 0.3NiS is 0.7). O _ 3 / ZrO _ 2 formed the structure of Ni-Co alloy particles dispersed on ZrO_2 support modified by lanthanum oxide. The bimetallic catalyst was coordinated by Ni and Co. It has the best catalytic performance in SRE reaction, including high activity, high hydrogen selectivity and good stability. This design idea has been widely used in the field of catalysis. This is because the type of carrier is tunable and the metal ions at the Agna B position in perovskite are also tunable. Ce_(0.5)Zr_(0.5)O_2 and macroporous Ce_(1-x)Zr_xO_2(x=0 were prepared by citric acid one-step method and PS template method, respectively. Using nickel oxide supported on different pore structure as catalyst precursor for ethanol reforming to produce hydrogen. O _ 2-supported nickel catalyst has the best catalytic performance in the reaction. Compared with the other two catalysts, the activity and stability are the best.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O643.36;TQ116.2

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