【作者】 秦玉；

【导师】 楼辉；

【作者基本信息】 浙江大学 ， 化学， 2014， 博士

【摘要】 近年来,生物质能源的开发利用正逐渐受到越来越多的关注,其中生物柴油是一种清洁可再生的生物质能源。在自然界中广泛存在、来源丰富,属可再生资源的植物油脂和柴油在结构组成上均含有长的碳链组分。柴油主要是指含10-22个碳原子的烃类混合物,燃烧热值高,是一种优良燃料。植物油脂主要是由一分子甘油和三分子分别含有8-22个碳原子的长链脂肪酸形成的,但是这类化合物存在含氧量高、粘度大、挥发性差、不稳定、不易存储等缺点,不适合直接用作内燃机燃料,而通过脱羧、脱羰、加氢脱氧等方法对植物油脂进行提质即可得到清洁的可再生柴油组分。本论文合成了一系列不同结构碳材料为载体负载的钼基催化剂,并以植物油选择性脱氧制备柴油类烃为目标对催化剂进行活性测试并对其脱氧反应机理进行了研究,详细分析了相关催化剂的物理化学性质并考察了不同碳载体及负载的钼基催化剂在植物油脱氧反应中的影响。主要研究结果如下：(1)考察了四种主要以sp2杂化的碳材料(石墨烯、碳纳米管、石墨和富勒烯)负载的钼基催化剂对玉米油的脱氧反应及异构化反应研究,运用“碳热氢还原法”合成出了不同物相组成的钼基催化剂。实验结果表明碳材料在反应中起着重要的作用,C渗入到Mo的晶格中可使Mo的d电子密度增加,而载体石墨烯的高导电性,又通过碳化钼中的碳传递给Mo,使它的d电子密度更大,从而增加了碳化钼的催化活性。(2)与共轭结构的碳材料作为对比,作者考察了三种无定型结构碳材料,介孔碳、以蔗糖为原料通过水热合成制备的活性炭和普通活性炭,负载的碳化钼催化剂对玉米油的脱氧反应效果及烃类产物分布规律。无定型碳材料负载的碳化钼催化活性低于共轭结构的石墨烯和碳纳米管为载体的碳化钼催化活性,作者推断其原因主要是碳的价电子杂化轨道及碳原子的排列结构不同,rGO的碳原子的价电子通过sp2杂化轨道成间层或若干层二维结构,活性炭中碳原子的价电子主要以sp3、部分以sp2排列的三维结构,其作为催化剂载体后对活性组分的影响不同导致催化活性的差别。(3)通过“碳热氢还原法”成功制备出了碳纳米纤维负载的碳化钼催化剂(Mo2C/CNF),碳纳米纤维具有与碳纳米管类似的物化性质,并且价格低廉。以脂肪酸甲酯为模型化合物研究了碳化钼催化剂的脱氧反应活性,并考察了对真实的植物油体系在超临界正己烷中的脱氧反应过程。以脂肪酸酯、脂肪酸和烯烃作为探针分子,讨论了脂肪酸酯在碳化钼催化剂上转变为烷烃的反应机理,为进一步阐明植物油脂脱氧制备柴油类烃的反应过程提供理论基础。(4)以石墨和活性炭为碳源,采用“碳热氢还原法”合成出了添加含N元素C3N4的混合碳材料负载的碳化钼催化剂,通过XRD、Raman和TEM分析初步考察了添加和不添加N元素对碳化钼催化剂形成的影响。比较了两类催化剂对玉米油催化活性及目标产物选择性的影响,并考察了碳材料负载的碳化钼催化剂对植物油的脱氧反应机理。更多还原

【Abstract】 In recent years, development and utilization of biomass-based energy resources is a hot domain all over the world. Biodiesel is a clean and renewable source of biomass. Vegetable oils, a rich source of renewable resources and existing widely in nature, have the similar structure of diesel that both contain long carbon chain components. Diesel oil is an excellent fuel, which is primarily a mixture of hydrocarbons containing10-22carbon atoms, high heat value of combustion. Vegetable oils are mainly composed of free fatty acids and their corresponding triglycerides. However, they are not suitable for direct combustion in modern diesel engines due to high oxygen content, high viscosity, high cloud point and low stability. Hence natural oils must be upgraded with decarboxylation, decarbonylation or hydrodeoxygenation to obtained diesel-like hydrocarbons.In the present dissertation, we investigated the selective deoxygenation of vegetable oils over a series of carbon materials supported molybdenum-based catalysts. Detailed analysis of the physical and chemical properties of catalysts including their preparations, characterizations, performance tests and corresponding reaction mechanisms were given in the thesis. Some conclusions drawn from the work are provided as follows:(1) Hydrodeoxygenation and isomerization of maize oil were performed in an autoclave using different carbon materials, such as graphene (rGO), carbon nanotubes (CNTs) graphite (G) and fullerene (C60), as supported molybdenum-based catalysts. Nanostructured molybdenum-based catalysts with different phase compositions were prepared by carbothermal hydrogen reduction (CHR) method at different temperature and characterized by Raman, N2adsorption isotherms, SEM, TEM, XRD, XPS, NH3-TPD and H2-TPD. The sp2hybridized carbon materials (rGO, CNTs, G and C6o) and the sp2and sp3hybridized AC carbon material were selected as supports to compare the catalytic activity of molybdenum-based catalysts. Carbon supports played an important role in participating in the reaction, and the Mo/rGO-700catalyst exhibited the best catalytic activity in the hydrodeoxygenation of maize oil. (2) Three kinds of amorphous carbon material structure, order mesoporous carbon, one kind of activated carbon prepared by hydrothermal synthesis and ordinary activated carbon, supported molybdenum-based catalysts were compared the catalytic activity of deoxygenation of maize oil. A preliminary discussion of the structure of the carbon materials in the corresponding molybdenum carbide catalyst prepared for catalytic activity of the deoxygenation reaction was mentioned.(3) Molybdenum carbide catalyst with different loading on carbon nanofibers (Mo2C/CNF) were successfully prepared by "carbothermal hydrogen reduction method". The high deoxygenation activity was obtained on model compound and real vegetable oil system in supercritical n-hexane process. Fatty acid esters, fatty acid and olefin molecules were selected as probes to explore the reaction process of the fatty acid esters into alkanes on molybdenum carbide catalyst, and there was no deactivation detected after five consecutive tests. Based on comprehensive analysis to gas and liquid products, the deoxygenation mechanism of fatty acid esters was proposed, the hydrodeoxygenation was the main reaction route.(4) With graphite and activated carbon as carbon source, the N-added molybdenum carbide catalysts were synthesized by the "carbothermal hydrogen reduction method" and characterized by XRD, Raman and TEM. Preliminary study of the effects of adding or not adding N element on the formation of molybdenum carbide catalyst was carried out. The corresponding catalytic activity in the hydrodeoxygenation of maize oil were compared, the N-added in the catalysts to some extent in favor to improve the activity of the hydrodeoxygenation of maize oil.更多还原