【作者】 李强；

【导师】 张学勤；

【作者基本信息】 华侨大学 ， 工业催化， 2014， 硕士

【摘要】 α-酮酸酯经不对称催化加氢得到的手性α-羟基酸酯，广泛应用于手性药物、农药、香精香料及食品添加剂等精细化学品的合成中。氧化铝负载的铂催化剂在α-酮酸酯不对称加氢中能够取得优异的光学选择性，但重复利用性能不佳；介孔碳负载的铂催化剂重复利用性能突出，但光学活性较低。本文针对单一载体负载铂催化剂存在的缺点，将氧化铝和介孔碳结合起来，制备了一系列氧化铝-碳复合材料，并作为载体制备负载型铂催化剂，应用到α-酮酸酯（2-氧-4-苯基丁酸乙酯和丙酮酸乙酯）的不对称加氢反应中，考察了载体中氧化铝的量，催化剂制备过程中浸渍溶剂、还原方法对催化性能的影响，结合催化剂表征，得到以下主要结果：1．采用螯合辅助溶剂挥发共组装法制备氧化铝-碳复合材料，考察了氧化铝含量对复合材料结构性质的影响。通过热重分析、X-射线衍射仪、N2物理吸附以及透射电子显微镜表征发现，氧化铝均匀分散于介孔碳结构中，并且，引入氧化铝能够增强介孔碳骨架的结构刚性，当氧化铝含量为5wt%-15wt%时，复合材料具有有序的介孔孔道结构和较大的孔径。X-射线光电子能谱表征结果还发现，复合材料表面仍然存在较多的-C-O-基团，说明复合材料中碳组分未完全碳化。2．将氧化铝-碳复合材料作为载体用于负载铂纳米粒子，考察了载体中氧化铝含量、浸渍溶剂以及还原方法对催化剂结构性质及催化性能的影响。结果表明：a)介孔碳复合材料中氧化铝含量为10wt%-15wt%时，最有利于铂纳米粒子的分散，并且在催化剂高温还原之后仍能保持较好的孔道结构；氧化铝含量为15wt%的复合材料负载的铂催化剂在不对称加氢反应中催化性能最好，在2-氧-4-苯基丁酸乙酯不对称加氢中取得最高84.8%的光学收率，优于传统Pt/Al2O3和Pt/C催化剂，在丙酮酸乙酯不对称加氢中也能取得最高87.5%的光学选择性，优于传统Pt/C催化剂。b)研究铂前体三种不同浸渍溶剂对催化剂性质的影响时发现，乙醇作为浸渍溶剂时得到的催化剂铂纳米粒子最小，乙醇和水混合溶剂制备的催化剂铂粒子最大；而水作为浸渍溶剂时得到的铂纳米粒子尺寸大小最有利于其在2-氧-4-苯基丁酸乙酯和丙酮酸乙酯不对称加氢反应中取得高的光学选择性。c)考察一步高温还原和液相还原对催化剂性能影响时发现，不同的还原方法对催化剂结构性质、表面元素及含量等有很大影响；还原温度的升高和预先的液相还原均会导致催化剂结构的破坏，并减少催化剂表面残余氯的量；600℃氢气直接还原的催化剂表面无残余氯的存在，并且表现出最优的催化性能。d)在最优条件下（氧化铝含量为15wt%的复合载体、氯铂酸水溶液以及600℃一步氢气还原）制备催化剂，并考察其重复利用性能，发现复合材料负载的铂催化剂具有优异的重复利用性能，其在2-氧-4-苯基丁酸乙酯和丙酮酸乙酯不对称加氢中均能重复21次以上而活性没有明显下降，优于传统的Pt/Al2O3催化剂。更多还原

【Abstract】 Asymmetric hydrogenation of α-ketoesters have featured considerably in thesynthesis of enantiomeric purity α-hydroxy esters, which play extremely importantroles in synthesizing chiral drugs, agrochemicals, fragrances and food addictives. Inthe enantioselective hydrogenation of α-ketoesters, Al2O3supported Pt catalystsshowed superior catalytic performance but inferior reusability, while mesoporouscarbon supported Pt catalysts obtained opposite results. In order to solve these defectsof single component supported Pt catalysts, we studied the combination of Al2O3andmesoporous carbon. A series of alumina-carbon composites were synthesized andused as supports of Pt nanoparticles for the asymmetric hydrogenation of ethyl2-oxo-4-phenylbutyrate and ethyl pyruvate. Effects of alumina contents in thecomposites, impregnation solvents and reduction methods on catalytic performancewere investigated. Some main conclusions are as follows:1. A new procedure, chelate-assisted solvent vaporization co-assembly method,was used for synthesizing alumina-carbon composites, and effects of aluminacontents on composites structure properties were investigated. Studies byThermogravimetry, X-ray Powder Diffraction, N2sorption and Transmission ElectronMicroscopy revealed that alumina was dispersed in carbon structure uniformly, andthe incorporation of alumina enhanced the structure rigidity of mesoporous carbon.When the alumina contents were between5wt%and15wt%, the composites hadordered mesoporous structure and big pore size. The results of X-ray PhotoelectronSpectroscopy showed that many-C-O-groups still retained on the surface ofcomposites, indicated that the carbon component in the composite was not fullycarbonated.2. As-prepared alumina-carbon composites were used as supports of Ptnanoparticles, and effects of alumina contents, impregnation solvents and reductionmethods on structure properties and catalytic performance of Pt supported catalystswere investigated. a) Carbon composites incorporated with10-15wt%alumina were favorable for the high Pt dispersion and retained the mesostructure after hightemperature reduction. The cinchnidine-modified Pt/15wt%alumina-carbon showedbest catalytic performance, obtaining84.8%and87.5%enantioselectivity in theasymmetric hydrogenation of ethyl2-oxo-4-phenylbutyrate and ethyl pyruvate,respectively. b) Effects of impregnation solvents on catalytic properties duringcatalyst preparation were investigated. Ethanol solution of H2PtCl6was favorable forthe high Pt dispersion, while the catalyst prepared from the ethanol and water mixedsolution of H2PtCl6showed slight aggregation in Pt nanoparticles. The results ofasymmetric hydrogenation reactions revealed that the Pt particle size of the catalystprepared from the aqueous solution of H2PtCl6was in favor of high excessenantiomeric. c) Effects of one-step high temperature reduction and aqueousreduction were carried out as well. Different reduction methods influenced thestructure properties and catalytic performance obviously. The increase in reductiontemperature and pre-aqueous reduction both destroyed the ordered mesostructure andreduced the chlorine residuals on the surface of catalysts. The catalyst directlyreduced in hydrogen at600oC had no surface clorine residuals and showed superiorcatalytic performance. d) Pt/alumina-carbon catalyst which was prepared with theoptimal conditions (carbon composites incorprated with15wt%alumina, watersolution of H2PtCl6and one-step reduction at600oC) showed excellent reusability,which could be reused for21times without distinct loss in enantioselectivity andactivity for the enantioselective hydrogenation of ethyl2-oxo-4-phenylbutyrate andethyl pyruvate.更多还原