【作者】 王文举；

【导师】 王亚权；

【作者基本信息】 天津大学 ， 化学工艺， 2009， 博士

【摘要】 氢气作为一种高效清洁能源可同时解决能源危机和环境污染这两大难题。近几十年来,燃料电池技术的迅速发展为氢的应用提供了更广泛的空间。但由于氢气是二次能源,对制氢技术有着极强的依赖性。传统的制氢技术以化石原料为主,制氢过程存在着原料不可再生、温室气体排放等问题。而乙醇的重整制氢作为生物质间接制氢的方法之一,具有可再生性和CO2闭合循环(不净排放CO2)的特征,因此研究开发乙醇制氢具有重要的实际意义。本文应用热力学方法对乙醇水蒸汽重整、部分氧化和二氧化碳重整这三个重要乙醇制氢方法进行研究;用不同方法制备了一系列含镍催化剂,考察其在乙醇水蒸气重整反应中的催化性能;运用BET、TPR、XPS和XRD等多种技术对催化剂的宏观结构、表面性质、还原性以及镍与载体之间的相互作用等进行了研究,并把表征结果与催化剂的性能进行了关联。热力学计算表明,对于乙醇直接裂解(DE)、乙醇水蒸气重整反应(SRE)、乙醇部分氧化反应(POE)和乙醇二氧化碳重整反应(DRE),温度的升高有利于H2和CO的生成,不利于CH4和固态C的生成;惰性组分的添加有利于H2的生成和固态C的消除;压力的升高不利于H2的生成和固态C的消除;优化以后的操作条件适合为熔融碳酸盐燃料电池和固态氧化物燃料电池供原料。热力学和密度泛函(DFT)研究表明,乙醇裂解的路径为乙醇裂解生成甲烷和甲醛,甲醛再裂解生成H2和CO;在SRE中,生成的氢气有一部分来源于水分子中的氢,水分子中的氢也参与了生成甲烷、甲醛和甲醇。用泡沫镍制备的Ni金属催化剂催化SRE,酸处理后比表面增大、反应活性升高;温度的升高促进了H2和CO的生成,但是H2和CO的产率低于热力学平衡值;H2O/C2H5OH比的升高导致H2和CO2产率增加、CO产率先升高后下降、甲烷产率单调减少;液时空速的增大对H2和CO的生成不利。用浸渍法制备的10NixCu/MgO/γ-Al2O3系列催化剂催化SRE , 10Ni5Cu/MgO/γ-Al2O3表现出最优良的性能,923K时在该催化剂上乙醇转化率为100%,氢气收率为71%,并且有高的H2/CO比。增加水醇比有利于氢气和CO的生成,抑制甲烷的生成。随着液时空速的增加,氢气收率减少。利用DFT模拟了CO在纯金属Ni(111)表面上的吸附。结果表明,Ni(111)表面上桥式CO吸附有利,这种吸附方式使C–O键被最大程度地削弱;在CO向Ni供电的同时,Ni原子中的d电子有明显的反馈现象。由于Cu原子在Ni-Cu双金属催化剂表面上富集,而且Cu向Ni供电,使得CO分子中的C–O键加强,因而C–O键断裂生成炭的倾向得以抑制,所以Cu的加入提高了催化剂的抗积炭性能。C–O键裂解生成的炭减少,炭加氢生成甲烷的量也减少了。用共沉淀法、柠檬酸络合法和尿素燃烧法制备的含镍金属氧化物(NiO-ZnO,NiO-A12O3和NiO-MgO)催化剂催化SRE的结果表明,尿素燃烧法制备的NiO-MgO催化剂在低温(873K)下具有良好的活性;在液时空速达20 ml g-1 h-1时仍具有高活性和选择性。更多还原

【Abstract】 Hydrogen is an efficient and clean energy, which can simultaneously solve the energy crisis and environmental pollution. In the last few decades, the rapid development of fuel cell technology broadens the application of hydrogen. However, in the traditional hydrogen production methods, fossil materials are used, which are non-renewable and discharge greenhouse gases. The steam reforming of bio-ethanol is one of the indirect biomass to hydrogen ways, which is a CO2-closed cycle (not to generate new CO2). Research and development of hydrogen production from ethanol is of great theoretical and practical significance. In this paper, the thermodynamics of steam reforming of ethanol (SRE), partial oxidation of ethanol (POE) and carbon dioxide reforming of ethanol (DRE) were studied; a series of nickel based catalysts were prepared by different methods, characterized by BET, TPR, XPS and XRD, and studied in the ethanol steam reforming.The thermodynamic results showed that for the direct decomposition of ethanol (DE), SRE, POE and DRE, high temperature favored H2 and CO formation, but unfavored CH4 and coke formation; the addition of inert component favored H2 production and coke elimination; high pressure unfavored H2 production and coke elimination. The optimal operating conditions were found for the supply of fuels to molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC). The noncatalytic reaction path was investigated through Density Function Theory (DFT) and thermodynamic analysis. The results showed that ethanol is first decomposed to methane and formaldehyde, and then formaldehyde is converted to H2 and CO. In SRE, the hydrogen partially comes from the water molecules, and water is also involved in the production of methane, formaldehyde and methanol.The SRE was studied over Ni metal catalyst. It is found that acid treatment increased the surface area and activity of the catalysts; high temperature promoted the formation of H2 and CO, but the yields of H2 and CO were still lower than the thermodynamic equilibrium values; the increase of H2O/C2H5OH molar ratio increased the yields of H2 and CO2; increasing LHSV decreased the yields of H2 and CO. The SRE was also investigated over a series of 10NixCu/MgO/γ-Al2O3 catalysts prepared by an impregnation method. 10Ni5Cu/MgO/γ-Al2O3 exhibited excellent catalytic performance. Ethanol conversion rate and the hydrogen yield were 100% and 71% over this catalyst, respectively. The increase of water-to-ethanol molar ratio increased the yield of hydrogen, but decreased the yields of methane and CO. The increase of LHSV decreased the yield of hydrogen.The adsorption of CO on the surface of Ni(111) was investigated through DFT. The results showed that CO was easy to be adsorbed in a bridge mode on the surface of Ni(111), and C–O bond was weakened. There were appreciable electron feedbacks from Ni d orbits. With the addition of Cu, Cu enriched on the surface of the catalyst and donated electron to Ni, which made the C–O bond strengthen and therefore the carbon formation was restrained. Methane formation, resulting from the hydrogenation of deposited carbon, was reduced.The SRE was also investigated over Ni metal oxide catalysts prepared by precipitation, citric acid complexing and urea combustion methods. The results showed that NiO-MgO catalyst gave the highest activity and hydrogen yield at low temperatures; the activity of the catalysts did not change significantly with LHSV below 20 ml·g-1·h-1.更多还原