【作者】 夏水鑫；

【导师】 侯昭胤；

【作者基本信息】 浙江大学 ， 化学， 2014， 博士

【摘要】 随着经济的发展和人们环保意识的提高,开发和利用可再生能源成为全世界关注的热点。生物柴油具有原料来源广、环境友好、可再生、安全性高、可替代石化柴油等优点,已经成为化石燃料的重要补充,而且其生产规模逐年扩大。然而生物柴油生产过程中的主要副产物—甘油的产量严重过剩,因此,研究甘油的深加工技术具有重要的意义,其中甘油氢解制备丙二醇被广泛认为是一条具有重要应用前景的转化途径。目前文献报道的甘油氢解的催化剂主要可以分为贵金属催化剂和以Cu, Ni, Co为代表的非贵金属催化剂,其中铜基催化剂由于价格低廉和对1,2-丙二醇的高选择性而受到人们的青睐。因此,本论文以含铜水滑石为前驱体,通过可控的干燥、焙烧及还原等工艺制备了系列多功能催化剂,先后通过引入第二活性金属、优化催化剂的酸碱特性、引入骨架稳定助剂等手段对催化剂的结构、性能和反应活性进行了系统的调控和优化,并对反应机理进行了探究。研究得到的主要成果如下：先后采用Pd, Rh, Ru和Re作为第二活性金属,经水滑石前驱体制备出了系列高活性的贵金属-Cu双金属／固体碱催化剂,详细表征、研究了催化剂的结构和它们在甘油氢解反应中的活性。实验发现：引入第二活性金属可以大幅降低反应温度和反应压力,同时缩短了反应时间。表征结果发现：Pd等第二金属的加入可以促进Cu2+的还原、增加H2的吸附量。2.0MPa H2、180℃下反应10小时(h), Pd0.04Cu0.4/Mg5.56Al2O8.56催化剂上表面Cu原子的平均比活性达到9.7mol-gly/mol-Cu/h,1,2-丙二醇的选择性达97%以上。通过调控四组分水滑石前驱体(Cu0.4Zn5.6-XMgXAl2(OH)16CO3)中的Zn/Mg比,制备了一系列酸碱可调的Cu/Zn-Mg-Al催化剂,详细表征了这些催化剂的酸碱性、形貌、结构、铜的分散度、氢溢流以及甘油吸附等特性。实验发现：在Cu0.4/Zn0.6Mg5.0Al2O8.6催化剂上,表面Cu原子的平均比活性高达9.7mol-gly/mol-Cu/h (180℃,2.0MPa H2,10h),这一活性与贵金属Pd改进的Cu/固体碱催化剂的活性相当；同时,这个催化剂的重复使用活性良好。在上述结果的基础上详细探讨了甘油氢解反应的机理及催化剂的构效关系规律,这个规律可以简单地概括为：Cu/Zn-Mg-Al系列催化剂在甘油氢解反应中的活性主要取决于催化剂的碱性和铜的分散度,除此以外,ZnO与Cu之间的氢溢流作用也可以明显促进甘油的转化。针对前面研究中发现的水滑石基催化剂高温焙烧后层板无序堆积、比表面积低、金属利用效率低等问题,采用机械强度高、热稳定性好、具有氢溢流特性的多壁碳纳米管作为支撑,合成了结构稳定、具有高比表面积和双介孔结构的多壁碳纳米管柱撑的水滑石材料。表征结果发现：多壁碳纳米管(MWCNT)与水滑石层板的紧密接触促进了层板中Cu2+的还原和MWCNT到Cu表面的氢转移。这种催化材料在甘油氢解反应中展现出优异的催化活性,表面Cu原子的平均比活性最高可达17.2mol-gly/mol-Cu/h (180℃)为了有效解决催化剂回收和重复利用的难题,本文还进一步设计和制备出了具有磁性的核壳型Fe2O3@CuMgAl催化剂,并将其用于甘油氢解反应中。通过XRD、N2-全吸附、H2-TPR、SEM、TEM、CO2-TPD、XPS等表征手段发现：核壳型Fe2O3@CuMgAl催化剂中铜的分散度较高,同时,水滑石层板沿Fe203微球有序的生长也使得这些层板的热稳定性得到了很大程度的提高,这种磁性催化剂易分离、循环使用效率高。最后,我还尝试了采用原位氢转移手段在惰性氛围下进行1,2-丙二醇的合成反应,详细考察了Cu-Mg-Al催化剂的碱性、氢转移试剂的种类等对甘油氢解制备丙二醇的反应活性和机理的影响。实验发现,Cu是一种高效的氢转移催化组分,乙醇的脱氢和甘油的氢解主要发生在Cu的表面；催化剂的活性还取决于其碱性,碱性的增强也有利于氢转移反应的进行。采用乙醇作为氢转移试剂,Cu0.4/Mg6.28Al1.32O8.26催化剂上甘油的转化率可达95.1%,1,2-丙二醇的选择性高于90%(210℃)。更多还原

【Abstract】 Recently, much attention has been paid to the utilisation of renewable energy. Among them, biodiesel, which could replace petro-diesel, has been reported popularly all over the world for its safety and renewability. Biodiesel is produced from vegetable oils or animal fats via the transesterification process. Glycerol, as a major byproduct, is largely produced in this process. In recent years, with the expanding demand for biodiesel, glycerol is oversupplied. It is of great importance to convert glycerol into value-added chemicals. Hydrogenolysis of glycerol to propanediols (PDOs) has been regarded as one of the most promising processes.Cu-based catalyst has been investigated popularly for its lower price and high selectivity to1,2-propanediol (1,2-PDO) owing to its lower activity for C-C bond cleavage. The aim of this dissertation is to synthesize highly effective catalysts via layered double hydroxide (LDH) precursors under controlled drying, calcinations, and reduction. The main achievements of this work are:Highly effective bimetallic noble metal-Cu/solid base catalysts have been prepared from the LDH precursors by introducing a second active metal (Pd, Rh, Ru, Re). Characterizations disclosed that Pd, Rh, Ru, and Re promoted the reduction of Cu2+, enhanced its ability of adsorbing hydrogen, and lowered the reaction temperature, pressure and time significantly. The activity of surface Cu atoms in Pdo.o4Cuo.4/Mg5.56Al2O8.56reached9.7mol-gly/mol-Cu/h at180℃.A series of Cu/Zn-Mg-Al catalysts with different Zn/Mg molar ratios were prepared. The morphology, structure, acid-base properties, the dispersion of copper and hydrogen spillover were characterized. It was found that the acidity (and basicity) of these catalysts could be manipulated by adjusting the molar ratio of Zn/Mg. Cuo.4/Zn0.6Mg5.0Al2O8.6exhibited the best performance for hydrogenolysis of glycerol in aqueous solution at180℃. The calculated activity of surface Cu atom reached9.7mol-gly/mol-Cu/h, which was comparable to that of bimetallic Pd-Cu/solid base catalyst. It was concluded that the conversion of glycerol over Cu/Zn-Mg-Al catalyst depended strongly on both the basicity and the dispersion of Cu. At the same time, hydrogen spillover from ZnO to Cu also enhanced its performance. The catalyst could be recycled while maintaining a good catalytic activity. During the controlled thermal decomposition of LDH, the decomposition of interlayer anions and dehydroxylation of brucite-like sheets lead to the disordered stacking of lamellae. Certain places of the lamella could not be used efficiently owing to the overlap of lamellae. In order to solve this problem, multiwall carbon nanotube (MWCNT) was selected as the support, and a series of MWCNT-pillared layered Cu0.4/Mg5.6Al2O8.6materials with stable structure, doublet meso-pore channels and high surface area were fabricated and used for glycerol hydrogenolysis. Characterizations disclosed that the close contact of layered Cuo.4/Mg5.6Al2O8.6with MWCNT enhanced the reducibility of Cu2+. And the hydrogen spillover from MWCNT to Cu contributed to the conversion of glycerol. This material showed enhanced catalytic performance in glycerol hydrogenolysis reactions. The highest activity of surface Cu atom reached as high as17.2mol-gly/mol-Cu/h at180℃.Core-shell structured magnetic Fe2O3@CuMgAl LDH catalysts were synthesized for selective hydrogenolysis of glycerol. Characterizations of XRD, N2-adsorption, H2-TPR, SEM, TEM, CO2-TPD and XPS disclosed that the thermal stability of the LDH framework, the dispersion of Cu and its activity were enhanced simultaneously in the presence of Fe2O3. These magnetic catalysts could be easily separated by an external magnetic field and showed high efficiency in reuse.At last, synthesis of1,2-PDO with the required hydrogen produced from hydrogen donor molecule instead of H2was carried out. The reactions were performed over Cu-Mg-Al catalysts with different (Cu+Mg)/Al molar ratios. Different alcohols were selected as the hydrogen donors. It was found that the performance of Cu-Mg-Al catalysts for this reaction depended mainly on their basicity, and Cu was indispensable for this reaction because alcohol dehydrogenation was performed on Cu. With ethanol as the hydrogen donor, the conversion of glycerol over Cu0.4/Mg6.28Al1.32O8.26reached95.1%at210℃, and the selectivity of1,2-PDO is higher than90%in most experiments.更多还原