论文标题:负载型Ni-Ru双金属催化剂催化乙醇水蒸气重整制氢的研究
Study on Supported Ni-Ru Bimetallic Catalysts for Hydrogen Production from Ethanol Steam Reforming
论文作者
论文导师 石秋杰,论文学位 硕士,论文专业 物理化学
论文单位 南昌大学,点击次数 123,论文页数 70页File Size4610K
2007-12-12论文网 http://www.lw23.com/lunwen_2870992/
ethanol steam reforming;; hydrogen production;; Ni-Ru bimetallic;; composite support;; plasma
乙醇可以来源于农作物的发酵，为可再生的能源。生物乙醇生产简单且便宜，因此乙醇水蒸气重整制氢作为一种生产氢气的方法已受到越来越多的关注。本文采用浸渍法制备催化剂，考察了负载型Ni-Ru双金属催化剂在乙醇水蒸气重整制氢中的催化性能，研究了Ni-Ru不同的比例、不同载体以及复合载体中不同的金属氧化物的比例对双金属催化剂性能的影响，采用比表面积测定、氢气程序升温还原(H_2-TPR)、X射线衍射(XRD)、X射线光电子能谱(XPS)和热重(TG)等表征对催化剂的比表面积、还原性能、晶相、表面组成及价态和抗积炭能力进行了研究。本文还初步研究了等离子体处理制备Ni基催化剂在乙醇水蒸气重整制氢中的应用，考察了等离子体处理对催化剂的晶相，还原能力以及催化活性的影响。 在Ni-Ru／ZnO双金属催化剂中会形成Ni-Ru合金，Ru的氧化物的还原会促进NiO的还原，合金存在于催化剂的体相中，而不是在表面。活性测试表明，金属Ni断裂C-C键的能力强于Ru，而Ru基催化剂虽对乙醇脱水生成乙烯有较高的选择性，但可提高氢气的选择性。当Ni负载量为6wt％，Ru负载量为3wt％时，催化性能较好，400℃时，乙醇转化率已达100％，450℃时，CO的选择性最低(0.41％)，氢气的选择性为77.2％。 La的前驱体为La_2(CO_3)_3，XRD结果显示Ni-Ru／La_2O_2CO_3双金属催化剂中La是以六方晶形的La_2O_2CO_3的形式存在，同时在催化剂中有镍镧复合氧化物生成。研究结果表明La_2O_2CO_3为载体的催化剂表面存在晶格氧，这有利于提高催化剂的活性和氢气选择性。当Ni负载量为6wt％、Ru负载量为3wt％时，催化性能较好，400℃时乙醇转化率已达100％；450℃时，CO的选择性最低，为0.87％，氢气的选择性为85.9％。La_2O_2CO_3负载Ni-Ru双金属催化剂可有效降低积炭量，具有较好的稳定性。 6wt％Ni-3wt％Ru／ZnO-La_2O_2CO_3催化剂，当Zn∶La=1∶2时，催化剂的活性较好，在400℃时，乙醇转化率己达100％，在450℃时，CO的选择性最低，为0.57％，氢气的选择性为87.8％。这是由于相对于单一载体，晶格氧会在复合载体负载的催化剂表面富集。XRD和TPR结果显示，催化剂中会形成镍镧复合氧化物。 用等离子体处理制备了Ni／ZnO和Ni／La_2O_2CO_3，结果表明，等离子体处理不会改变催化剂中的晶相，但金属氧化物的颗粒会减小，金属与载体间的相互作用力变化不大。等离子处理制备可提高催化剂Ni／ZnO的反应活性和氢气选择性，但会降低Ni／La_2O_2CO_3的低温有催化活性和高温时对氢气的选择性。
Ethanol can be prepared from fermentation of agricultural residues and hence it is a renewable resource. Its production is simple and cheap and hence steam reforming of ethanol to produce hydrogen is attractive more and more. Ni-Ru bimetallic catalysts were prepared using impregnation method and the catalytic properties for hydrogen production from ethanol steam reforming were investigated in this thesis. The effects of different ratio of Ni-Ru, different supports and different ratio of metal oxide in composite support on catalytic properties of bimetallic catalysts were discussed. The catalysts were characterized by means of nitrogen adsorption-desorption, H_2 temperature programmed reduction(H_2-TPR), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and thermo gravimetric(TG) to study BET surface area, redox properties, phase structure, surface composition and valence and resistance to carbon deposition. The applications of Ni catalysts prepared by a plasma treated method in ethanol steam reforming were studied primitively. The influence of plasma treatment on phase of catalysts, redox properties and catalytic activities were investigated. In Ni-Ru/ZnO bimetallic catalysts Ni-Ru alloy maybe formed in the catalysts and the reduction of ruthenium oxide enhanced reduction of nickel oxide. Ni-Ru alloy existed in the bulk phase not on the surface of the catalysts. Activity test proved that the ability of Ni for rupture of C-C bond was stronger than that of Ru, and Ru was active in the ethanol dehydration reaction leading to the formation of ethylene. However, Ru could improve the selectivity of hydrogen. The catalyst with metal loading of 6wt%Ni and 3wt%Ru showed best performance. The ethanol conversion could reach 100% at 400℃. And CO selectivity was minimum of 0.41% at 450℃while the selectivity for hydrogen was 77.2%. The precursor of La was La_2(CO_3)_3 whereas XRD exhibited that La was in the form of hexagonal La_2O_2CO_3 in Ni-Ru bimetallic catalysts and there existed mixed oxide of Ni and La. The lattice oxygen existed on the surface of the catalysts supported on La_2O_2CO_3, which was benefit for improvement of catalytic activity and hydrogen selectivity. As ZnO supported catalyst, the catalyst with metal loading of 6wt%Ni and 3wt%Ru supported on La_2O_2CO_3 showed best performance. The ethanol conversion could reach 100% at 400℃, and CO selectivity was minimum of 0.87% at 450℃while the selectivity for hydrogen was 85.9%. Ni-Ru bimetallic catalysts supported on La_2O_2CO_3 could decrease the amount of carbon deposition and improve the stability of catalysts. ZnO-La_2O_2CO_3 mixed supports were prepared using impregnation method. The effect of different molar ratio of Zn and La in supported 6wt%Ni-3wt%Ru bimetallic catalysts on the catalytic performance was discussed. The results showed that the catalyst with molar ratio of Zn: La=1:2 performed best. The ethanol conversion was 100% at 400℃, and CO selectivity reached minimum of 0.57% at 450℃while the selectivity for hydrogen was 87.8%. XPS studies exhibited that lattice oxygen could be enriched on the surface of composite support compared with mono support. XRD and TPR showed that mixed oxide of nickel and lanthanum was formed and the integrity of lattice for hexagonal ZnO and La_2O_2CO_3 was damaged. Catalysts Ni/ZnO and Ni/La_2O_2CO_3 were prepared using plasma enhanced impregnation method. The phase of catalysts did not change after plasma treatment whereas the particle size of metal oxide could be decreased. TPR results exhibited that the interaction between metal and supported didn"t be changed greatly but the distribution of NiO was improved. The activity and hydrogen selectivity on Ni/ZnO prepared using plasma enhanced impregnation method were improved. However, the ethanol conversion decreased at low temperature and at a high temperature hydrogen selectivity decreased on the plasma-treated Ni/La_2O_2CO_3.
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