【作者】 王建强；

【导师】 范康年；

【作者基本信息】 复旦大学 ， 物理化学， 2005， 博士

【摘要】 环己烯是一种重要的有机合成中间体,具有活泼的双键,作为有机化工原料,可广泛应用于医药、农药、农用化学品、饲料添加剂、聚酯和其他精细化学品的生产,尤其环己烯的深加工产物环己酮和己二酸是合成聚酰胺纤维中大量使用的中间体。20世纪80年代以来,国外提出由苯选择加氢生产环己烯,并成功地实现了工业化。90年代以后,苯选择加氢制环己烯催化剂的重要性才引起我国大的科研单位、重点高校和石化公司的重视,但研究进展缓慢。开发具有自主知识产权的新催化体系,缩短我们和世界发达国家的距离,具有十分重要的意义。一方面,苯选择加氢制备环己烯具有重要的工业应用价值,另一方面,尽管许多金属被广泛应用于选择加氢领域,但是现有的理论也仅仅局限于某一些甚至特定反应,目前仍无系统和完善的理论来指导该领域的研究与生产。苯选择加氢催化理论上的研究也将为选择加氢领域研究提供进一步的信息和做出相应的贡献。 针对目前Ru催化剂的研究情况,本论文从催化剂的载体以及催化剂Ru活性中心修饰两个角度进行了研究。从载体角度出发,研究了以氢氧化物为载体的Ru催化剂,苯选择加氢反应结果表明,其催化性能显著优于相应氧化物负载的Ru催化剂,特别是Ru负载氢氧化铝催化剂。因此,对氢氧化铝的诸多性能进行了系统研究,并重点研究了Ru/AlOOH、RuB/Al₂O₃·xH₂O催化剂。采用溶胶凝胶法结合超临界流体干燥成功制备了一种δ-氧化铝纳米纤维,考虑到化学混和法容易制备高分散Ru催化剂的特点,探索了制备Ru/δ-alumina nanofibre的情况,并研究了其在苯选择加氢中的应用。从Ru活性中心角度出发,制备了一种RuZn/m-ZrO₂纳米复合催化剂,并研究了无机添加剂硫酸锌、有机添加剂甲醇以及添加第二金属组分对催化剂性能的影响;制备了粒径可控的一系列PVP-RuB胶粒催化剂,重点研究了RuB胶粒大小对苯选择加氢反应的影响。 论文的主要工作及结果如下: 一、Ru/氢氧化物催化剂制备表征及液相苯选择加氢反应初步研究 长期以来,氢氧化物因缺乏热稳定性而很少被用做催化剂的载体。近年来,一些催化工作者发现氢氧化物负载的Au催化剂具有较好的分散度,在低温CO氧化至CO₂更多还原

【Abstract】 Cyclohexene, which has a highly reactive double bond, could be used as an intermediate material for producing adipic acid, nylon-6, nylon-66, and fine chemicals. Cyclohexene can be made by several methods such as dehydration of cyclohexanol, hydrodehalogenation of halogenated cyclohexane, or dehydrogenation of cyclohexane. In any of the methods mentioned above, the starting materials are the compounds derived from aromatic hydrocarbons. These processes for producing cyclohexene require complicated multiple steps, the efficiencies are poor, thus leading to high production cost. A route running via selective hydrogenation of benzene to cyclohexene possesses the low price of the raw material, the simplicity of the process, along with the atomically economical character of the reaction. The Asahi chemical industry of Japan has commissioned a plant for manufacturing cyclohexanol using benzene to cyclohexene route. In china, Shenma group company also introduced this technology to build a plant, but had to pay high costs for Japan’s patent. Thus, the preparation of cyclohexene through such route is of great value academically and industrially.The hydrogenation of benzene to cyclohexane is thermodynamically much more favorable. Under normal conditions, there is a strong tendency of the reaction to proceed to cyclohexane in one step. Notwithstanding this difficulty, a search for the appropriate catalyst, additives and reaction conditions is on for maximizing the yield of cyclohexene. The hydrogenation capability of the catalyst should not be so strong that over-hydrogenation prevails, or so weak that reaction rate is low. Based on numerous works, it has been acknowledged that ruthenium is the most suitable metal for this reaction, and liquid phase reaction is the most promising in industrialization. Therefore, the present studies deal with the liquid phase hydrogenation of benzene to cyclohexene over a series of Ru novel catalysts.For the ruthenium catalyst, two aspects are selected to investigate benzene selective hydrogenation. On the one hand, we studied metal hydroxide supported Ru catalysts besides the generally traditional support. On the other hand, we studied some catalysts such as RuZn, PVP-RuB and the effect of strong metal support interaction on the catalysisperformance from the point view of Ru active center. Some new conclusions are drawn as the following,1. Metal hydroxide supported Ru catalyst and liquid phase hydrogenation of benzeneMetal hydroxide is seldom used as catalyst supports due to its thermal stability. Recently, some researchers found that Au catalyst supported on metal hydroxides displayed a good dispersity and catalysis performance in low temperature oxidation of CO to CO2. Additionally, reaction system of benzene selective hydrogenation contains a special phase, water phase. This prompts us to have an idea to investigate a series of metal hydroxide supported catalysts and make a preliminary study in benzene selective hydrogenation.A series of metal hydroxides supported Ru catalyst were prepared by coprecipitation and then followed by hydrogen reduction in liquid phase. The XRD, XPS characterizations suggested the catalyst was Ru/AIOOH, Ru/TiO2-nH2O, Ru/La(OH)3 and Ru/Mg(OH)2, respectively. The catalytic behavior in liquid phase selective hydrogenation of benzene to cyclohexene was studied and compared with that of the corresponding oxide supported catalyst reported in the literature. The metal hydroxide catalysts are found more reactive than the corresponding oxide supported catalyst, and the maximum yield of cyclohexene is also more than that over the latter.2. Aluminum hydroxide supported Ru catalyst and alumina supported catalyst(1) Aluminum hydroxide preparation and its hydrothermal stability1) Bayerite preparation and characterizationBayerite with irregular shapes was obtained by aging the precipitate from the reaction of aluminum nitrate and ammonia, but it is contaminated with a minor component of gibbsite, as evidenced by XRD, TG-DTA, and TEM results.2) Effect of hydrothermal conditions on boehmite formationThe transformation of bayerite to boehmite is attempted to carry out under different hydrothermal conditions. Unstirred condition resulted in uncompleted transformation, where about mass ratio of 1:1 of bayerite to fibrillous boehmite reached. The effect of the atmosphere in the autoclave on the boehmite properties has been studied. The air atmosphere leads to monodisperse boehmite nanocrystals, while the hydrogen causes the agglomeration of boehmite nanocrystals. Thesystem pressure acts on the crystal growth in this research. Boehmite plates commence to aggregate as increasing the system pressure to 4 MPa. On the other hand, a larger pore on the exterior surface of the boehmite under relative high pressure was created in comparison with that under autogenous pressure. The effect of atmosphere kind on the surface pore is not distinct in the same condition. 3) Transformation mechanism from bayerite to boehmiteTemperature-programmed technique was applied for the first time to detect the transformation process and revealed the crystal-transformation mechanism at different atmospheres. The fissuring of bayerite occurs parallel to the {001} crystal faces for both atmosphere at same temperature of 150°C. A monodisperse boehmite nanocrystal comes into being under air atmosphere, while the aggregates of boehmite nanocrystals were formed under hydrogen atmosphere, which arises from the positive role of hydrogen in bayerite dissolution (or decomposition).(2) Ru/AIOOH Catalyst: Its Preparation, Characterization and Benzene Partial Hydrogenation Behavior1) A novel 4 wt.% Ru/AIOOH catalyst was prepared by the coprecipitation method and characterized by XRD, TG/DTA, TEM and nitrogen physisorption.2) In liquid phase benzene partial hydrogenation, Ru/AIOOH catalyst exhibited the highest cyclohexene selectivity and moderate activity as compared to Ru/y-AhO-} catalyst prepared by calcining the titled catalyst or by the wetness impregnation method. It is suggested that the surface hydroxyl groups and the large pores in boemite are essential for a high yield of cyclohexene.(3) Colloidal RuB/AhC^-JcH^O catalyst for liquid phase hydrogenation of benzene to cyclohexene1) A colloidal RuB/A^Os-jcE^O catalyst has been synthesized through a combined coprecipitation-crystallization-reduction strategy and characterized in detail with techniques including ICP-AES, N2 physisorption, XRD, TG/DTA, PSD and TEM.2) The catalytic behavior in liquid phase selective hydrogenation of benzene to cyclohexene was studied and compared with that of the RuB/y-A^Os catalyst prepared by the wetness impregnation method. The RUB/AI2O3XH2O catalyst is found more reactive than the RuB/y-AkOs catalyst, and the maximum yield of cyclohexene is about fourfold of that over the latter. The better activity of thecolloidal catalyst is assigned to the higher dispersion of the smaller RuB particles, whereas its superior selectivity is attributed to the improved hydrophilicity due to higher content of structural water and surface hydroxyl groups.3. Preparation of alumina nanofiber and Ru/5-alumina nanofiber catalyst(1) Attempts have been made to prepare alumina nanofibers by hydrolyzing aluminumnitrate in the presence of hexamethylenetetramine (HMTA) followed by the supercritical fluid drying (SCFD) process. The samples were characterized by XRD, TEM and nitrogen physisorption. The results show that 8-AI2O3 nanofibers with diameter of 2 nm, length of 50 run and with BET surface areas of 412.6 m2-g"’ were successfully synthesized. The thermal evolution of the fibers and the role of hexamethylenetetramine were also briefly discussed.(2) Introducing the Chemical mixing method and in combination with the sol-gel-SCFD process, we prepared a Ru/5-alumina nanofiber catalyst. The results of characterization suggest Ru particles were very large, approximately to 25 nm, which may be derived from the crystal growth in high temperature calcination and the following reduction. The benzene hydrogenation over such catalyst produced a low cyclohexene yield.4. Zirconia supported Ru catalysts and its application in selective hydrogenation of benzene to cyclohexene(1) Partial hydrogenation of benzene to cyclohexene on a RuZn//n-ZrO2 nanocomposite catalystA RuZn//ra-ZrO2 nanocomposite catalyst for benzene partial hydrogenation to cyclohexene was prepared by coprecipitation of ruthenium trichloride and zirconium oxychloride with ammonia, followed by hydrogen reduction in an aqueous zinc sulfate solution. By use of TEM, XRD and X-ray photoelectron spectroscopy (XPS), the reduction of zinc cation to metallic zinc and the transformation of zirconium hydroxide to monoclinic zirconia were proposed and explained. The hydrogenation parameters, such as the amount of zinc sulfate in the pretreatment process, the hydrogenation temperature, the stirring rate, and the hydrogen pressure, influenced the yield of cyclohexene. The pronounced更多还原