【作者】 刘建良；

【导师】 乔明华；

【作者基本信息】 复旦大学 ， 物理化学， 2010， 博士

【摘要】 环己烯是一种重要的有机合成中间体,广泛应用于医药、农药、农用化学品、饲料添加剂、聚酯等精细化学品的生产,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重要的中间体。工业上获得环己烯的方法有环己醇脱水、卤代环己烷脱卤化氢、环己烷脱氢等。这些方法普遍存在着生产工艺流程复杂、得率低、成本高等缺点,而通过苯部分加氢制备环己烯途径由于原料苯价格低廉、操作过程简单、符合原子经济性而备受人们的关注。1988年10月,旭化成公司(Asahi Chemical Ind.)在日本水岛率先建成了世界上第一套苯部分加氢制环己烯的工业化装置并对该技术严格保密。我国神马集团尼龙66盐厂于1996年引进了旭化成的技术,但是需要付昂贵的专利和催化剂购买费用,因而开发具有自主知识产权的新催化剂体系,具有十分重要的学术研究和工业应用价值。然而从热力学上看,苯加氢反应倾向于生成环己烷。为了获得高的环己烯得率,人们对催化剂活性组分、修饰剂、反应条件等做了大量的研究工作。现在已经证实,Ru金属是该反应最适宜的催化剂,而液相加氢反应最具有工业应用前景。因此本论文主要围绕高压液相反应来研究新型Ru催化剂在苯加氢反应中的催化性能,从Ru活性位修饰、反应液修饰以及催化剂载体的选取与制备几个方面进行了研究。从Ru活性位修饰出发,以介孔材料SBA-15为载体,通过双溶剂法制备了负载型Ru催化剂,并添加La、Ce助剂对催化剂进行改性,可明显提高环己烯的得率。从反应液修饰出发,该反应通常需要添加ZnSO4来抑制苯加氢活性和提高环己烯的选择性,本工作则首次报道了CdSO4与ZnSO4添加剂的协同作用,可以进一步提高环己烯的选择性。从催化剂载体出发,为了获得高的环己烯得率,要选择亲水性的载体。我们采用水热合成方法制备了MgAl2O4载体并负载Ru进行反应,发现催化剂的稳定性得到明显提高。由于ZrO2有着丰富的表面缺陷,同时具有弱酸、弱碱和氧化还原性,并在苯加氢反应中是一个非常好的载体和分散剂,本工作一方面从商业ZrO2着手,研究了双金属催化剂体系(RuPdB/ZrO2、RuPtB/ZrO2)对苯加氢反应的影响；另一方面针对商业ZrO2的比表面积低、不同方法所得ZrO2的晶型、比表面积和表面酸碱性不同的特点,制备了单斜与四方两种晶型的ZrO2作为载体,负载RuB研究了载体晶型和表面酸碱性对液相苯加氢反应的影响。自从1992年美国Mobil公司的研究人员宣布合成了一类全新的介孔硅(铝)分子筛M41S系列以来,介孔SiO2由于其较大的比表面积、较窄的孔径分布以及规整的孔道结构等特征而成为一种优良的载体,在催化加氢、氧化等领域显示了广泛的应用。但介孔SiO2作为载体来制备应用于苯部分加氢的Ru催化剂则鲜有报道。同时对于Ru催化剂而言,通常需要添加助剂来抑制活性和提高环己烯的选择性。中国拥有丰富的稀土资源,而稀土元素在催化加氢反应中能够显示出很好的助剂效果。因而本论文首先研究了La、Ce修饰的Ru/SBA-15催化剂对苯加氢反应的影响,并对催化剂进行了XRD、TEM、TPR、XPS等一系列表征,结合苯加氢反应数据,得到如下结论：1)通过双溶剂法制备的RuCe/SBA-15、RuLa/SBA-15催化剂在液相苯加氢反应中比Ru/SBA-15催化剂可获得更高的环己烯得率,La修饰的催化剂显示了最好的效果。在反应温度为413K,氢气压力为4.0 MPa,硫酸锌浓度为0.42M,硫酸镉浓度为1.56×10-3M时,环己烯得率可以达到57.4%,为目前所发表文献中的最高值。2)Ce、La的修饰减少了暴露在催化剂表面的Ru活性位数量,增加了金属Ru上的电子密度,提高了催化剂的亲水性,均有利于获得高的环己烯得率。3)通过对RuLa/SBA-15-0.8催化剂在不同反应温度和氢气压力下的催化性能研究,确立了合适的反应温度与氢气压力范围。反应温度的影响归因于对环己烯在催化剂表面的脱附和环己烯在薄水层中溶解度的影响,氢气压力的影响归因于氢分子与苯分子在催化剂表面的竞争吸附。对于液相苯加氢反应,为了获得高的环己烯得率,通常需要在反应液中加入添加剂。添加剂分为两种类型：有机添加剂和无机添加剂。目前实验室和工业生产中应用较多和比较成功的是无机添加剂ZnSO4,而且目前所发表的文献和专利均侧重于单一添加剂的加入,关于两种添加剂的协同作用未见报道。前期的研究表明,CdSO4添加剂很容易引起催化剂失活,而我们通过研究发现,对于RuLa/SBA-15-0.8催化剂,通过控制一定的CdSO4浓度,可以起到非常好的修饰效果,在硫酸镉浓度为1.56×10-3M时,环己烯得率可达27.5%。我们同时在反应体系中添加ZnSO4以期来进一步提高环己烯的选择性,在硫酸锌浓度为0.42M时,环己烯得率达到最高,为57.4%。而单独ZnSO4添加剂在其最佳浓度为0.42M时,环己烯得率为38.9%。两种添加剂的协同作用效果明显优于单一添加剂的修饰效果。为了阐释添加剂在反应中的作用,我们通过量化计算Cd2+、Zn2+离子与苯和环己烯之间可能形成的构型与能量,结合实验数据,得到如下结论：CdSO4更倾向于直接修饰催化剂的活性位,一方面Cd2+离子对催化剂的活性位起到明显的物理阻塞作用；另一方面Cd2+离子会同时抑制苯分子和环己烯分子在催化剂表面的吸附。相对于苯的吸附,对环己烯吸附的抑制更明显；ZnSO4的主要作用为稳定液相中间产物环己烯,加速其脱附并且抑制其再吸附,从而获得较高的环己烯得率。SBA-15系列催化剂可以获得较高的环己烯得率,但是其较低的水热稳定性导致催化剂寿命较短,因而限制了其应用。而MgAl2O4是一种化学和水热性能都非常稳定的材料,在合成氨、乙醇重整制氢、水煤气变换等催化反应有着广泛的应用。因此我们采用水热合成方法制备了MgAl2O4材料,并经过不同的焙烧温度处理以获得尖晶石晶相。液相苯加氢活性测试表明,1023K焙烧处理后的MgAl2O4负载的Ru催化剂显示了最好的效果。在反应温度为413K,氢气压力为4.0 MPa,硫酸锌浓度为0.28M,硫酸镉浓度为0.39×10-3M时,环己烯的最高得率可以达到38.5%,明显高于相同方法制备的Ru/MgO和Ru/Al2O3催化剂上所得环己烯的得率,而在Ru/Al2O3催化剂上所得环己烯的得率也比在Ru/MgO催化剂上的高Ru/MgAl2O4-1023催化剂套用3次以后,环己烯得率没有明显的下降,说明催化剂的稳定性得到明显改善,但是环己烯的最高得率低于修饰的Ru/SBA-15催化剂。环己烯得率的不同主要归因于载体亲水性的不同,亲水性载体负载的催化剂更有利于环己烯的生成,载体表面酸碱性的不同同样有较大影响。Ru/MgAl2O4系列催化剂上的环己烯得率与工业预期值有一定的差距,同时大量文献和专利表明,ZrO2是液相苯加氢反应很好的催化剂载体和分散剂。为了获得高的环己烯得率,通常需要对Ru催化剂添加助剂进行修饰。目前的助剂主要围绕Zn、Fe、Co、Ni及稀土元素开展研究,对贵金属元素的修饰作用报道极少。通过选择合适的贵金属元素,与Ru金属之间形成合金(RuPd、RuPt),而合金的形成(RuPd)对双金属催化剂在二甲苯、硝基苯等芳香烃加氢反应中显示了很好的促进效果。本节从商业ZrO2着手,添加Pd、Pt元素对RuB/ZrO2催化剂进行改性,研究了双金属催化剂对液相苯加氢反应的影响。苯加氢反应结果表明,Pd、Pt元素的加入可明显提高反应活性和环己烯得率,环己烯的最高得率由38.5%(RuB/ZrO2)提高到43.8%(RuPdB/ZrO2-0.2)和44.2%(RuPtB/ZrO2-0.15),相应地达到最高环己烯得率的反应时间则由80 min(RuB/ZrO2)缩短为60 min(RuPdB/ZrO2-0.2)和45min(RuPtB/ZrO2-0.15)。催化性能的提高归因于催化剂热稳定性、活性组分分散度的提高和表面合金的形成。商业ZrO2的比表面积很低(<10m2·g-1),且大多数为单斜晶型。对于液相苯加氢反应,催化剂载体的比表面积同样对反应性能的影响较大。文献中有较多关于ZrO2的合成方法,不同制备方法所得ZrO2的晶型、比表面积和酸碱性差别较大。因而我们制备了单斜与四方两种晶型的ZrO2作为载体并负载RuB,研究了载体晶型、表面酸碱性对液相苯加氢反应的影响。Py-IR研究发现,单斜ZrO2(ZrO2-M)同时具有Br(?)nsted酸中心和Lewis酸中心,而四方ZrO2 (ZrO2-T)只有Lewis酸中心。在相同的反应条件下,将经过873K焙烧处理的ZrO2-T和ZrO2-M作为载体负载RuB,应用到苯加氢反应中。环己烯的最高得率分别为46.6%(RuB/ZrO2-T-873)和37.8%(RuB/ZrO2-M-873),说明ZrO2-T-873负载的催化剂更有利于环己烯的生成。结合实验数据与文献报道,我们认为,吸附在Br(?)nsted酸中心上的苯易与来自金属活性中心的溢流氢作用生成环己烷,从而导致环己烯得率较低。本论文首次报道了ZrO2载体酸性位的不同对苯加氢反应的影响,该工作为下一步的深入研究做了很好的铺垫,并表明RuB/ZrO2-T-873系列催化剂可能有着很好的工业应用前景。更多还原

【Abstract】 Cyclohexene, which has a highly active double bond, is widely used as an intermediate for producing medicine, pesticide, agrochemical, feed additive, polyester fine chemicals etc, especially for the synthesis of polyamide fibre through its intermediates, cyclohexanone and hexanedioic acid. Cyclohexene can be made by several methods such as dehydration of cyclohexanol, hydrodehalogenation of halogenated cyclohexane, or dehydrogenation of cyclohexane. These processes for producing cyclohexene have disvantages of complicated multiple steps, low yield, and high production cost. A route via partial hydrogenation of benzene to cyclohexene possesses the low price of feedstock, the simplicity of the process, along with the atomically economical character of the reaction. The Asahi Chemical Industry of Japan has commissioned the first plant in the world for manufacturing cyclohexene from the partial hydrogenation of benzene route since Oct. 1988. In China, Shenma Group Company introduced this technology in 1996, but had to pay high costs for the patent and catalyst. Thus, the development of efficient catalyst system is of great significance academically and industrially.However, the hydrogenation of benzene to cyclohexane is thermodynamically much more favorable. Notwithstanding this difficulty, a search for the appropriate catalyst, additives and reaction conditions is on for maximizing the yield of cyclohexene. Based on numerous works, it has been acknowledged that ruthenium is the most suitable catalyst, and the liquid phase reaction is the most promising for industrialization. Therefore, we prepared a series of novel Ru catalysts and tested their catalytic performance in the liquid phase hydrogenation of benzene to cyclohexene.In order to promote the Ru active center, by using SBA-15 as support, we prepared the catalyst by the "two solvents method", and modified the catalyst by La or Ce; the yield of cyclohexene could be improved greatly. As to the reaction modifier, it is generally needed to add ZnSO4 to lower the catalytic activity and improve the selectivity to cyclohexene. For the first time we reported the synergistic effect of ZnSO4 and CdSO4 modifiers, which can efficiently improve the selectivity to cyclohexene. As to the catalyst support, in order to improve the yield of cyclohexene, we choose the support with a hydrophilic character. We prepared the MgAl2O4 spinel material by a hydrothermal method, after being impregrated with Ru, the stability of the catalyst was improved greatly. ZrO2, which has abundant surface defects, weak acid site, weak base site and re-dox character, is an excellent catalyst support and dispersant in the partial hydrogenation of benzene. On one hand, by using commercial ZrO2 as support, we studied the bimetallic effect (RuPdB/ZrO2, RuPtB/ZrO2) on the partial hydrogenation of benzene. On the other hand, considering the low surface area of commercial ZrO2, and different methods available to prepare ZrO2 with different crystal structure, surface area and surface acid-base character, we synthesized two kinds of ZrO2 materials (monoclinic and tetragonal) as supports for RuB catalysts, and studied the effect of crystal structure and surface acid-base character of the support on the liquid phase hydrogenation of benzene. The main results are summaried as follows:Since the discovery of M41S mesoporous materials by Mobil’s Company in 1992, mesoporous materials show wide applications in catalytic hydrogenation, oxidation fields due to its high surface area, narrow pore size distribution and uniform pore structure. But there are few reports about the preparation of Ru catalysts by using mesoporous silica as support for the liquid phase hydrogenation of benzene. Meanwhile, for the Ru catalyst, it is generally needed to add promoter to lower its catalytic activity and improve the selectivity to cyclohexene. China has abundant rare earth resources, which show excellent promoting effect in the catalytic hydrogenation reaction. So, we first studied the effect of La or Ce promoter on the Ru/SBA-15 catalyst in the liquid phase hydrogenation of benzene to cyclohexene. Combing with the XRD, TEM, TPR, XPS characterizations and reaction results, the following conclusions could be drawn:1) The RuCe/SBA-15 and RuLa/SBA-15 catalysts prepared by the "two solvents method" showed much higher selectivity to cyclohexene compared with un-modified Ru/SBA-15 catalyst, with La promoter showing the best result. The maximum yield of cyclohexene could reach 57.4% at 413 K of reaction temperature,4.0 MPa of hydrogen pressure,0.42 M of ZnSO4 and 1.56×10-3 M of CdSO4.2) The modification of Ce or La promoter reduced the surface Ru active sites; improved the electron density of Ru and the hydrophilicity of the catalyst, all favorable for the formation of cyclohexene.3) The effect of reaction temperature and hydrogen pressure was studied over the RuLa/SBA-15-0.8 catalyst. The reaction temperature influences the desorption of cyclohexene from the catalyst surface and the solubility of cyclohexene in the water thin film, while the effect of hydrogen pressure was due to the competitive adsorption of hydrogen and benzene molecule on the catalyst surface.In order to improve the yield of cyclohexene, the addition of a modifier to the reaction system is indispensable during the liquid phase hydrogenation of benzene. Generally, there are two kinds of reaction modifiers:organic modifier and inorganic modifier. ZnSO4 has been regarded as the most efficient modifier and all published documents (patents) have focused on the promoting effect of a single modifier. There are no reports about the synergistic effect of two modifiers. In the present work over the RuLa/SBA-15-0.8 catalyst, we found that by controlling the concentration of CdSO4, a much better yield of cyclohexene could be obtained, and a combination of CdSO4 and ZnSO4 performed much better than either of them alone. In order to elucidate the individual role of CdSO4 and ZnSO4 in the reaction, we fell to theoretical calculation to obtain the information about the interactions of Cd2+ and Zn2+ ions with benzene and cyclohexene. Based on experimental data and theoretical calculations, we concluded that CdSO4 acted as surface modification, suppressing more the adsorption of cyclohexene than that of benzene, while the function of ZnSO4 was mainly the stabilization of cyclohexene in the liquid phase, accelerating the desorption as well as hindering the re-adsorption of cyclohexene, thus improving the yield of cyclohexene.Although a high yield of cyclohexene could be obtained by using Ru/SBA-15-series catalysts, but due to the low hydrothermal stability of SBA-15 which results in its poor catalyst stability. Spinel is a kind of material with good chemical and thermal stability, which shows wide applications in ammonia synthesis, ethanol reforming and WGSR reactions etc. We prepared the MgAl2O4 material by a hydrothermal method and calcined at different temperatures to obtain better crystal structure of spinel. The catalyst prepared by using MgAl2O4 calcined at 1023 K as support showed the best result in the liquid phase hydrogenation of benzene, with the maximum yield of cyclohexene reaching 38.5% at 413 K of reaction temperature,4.0 MPa of H2 pressure,0.28 M of ZnSO4 and 0.39×10-3 M of CdSO4, much higher than the corresponding values on Ru/Al2O3 and Ru/MgO catalysts. Under the same reaction conditions, the maximum yield of cyclohexene on the Ru/Al2O3 catalyst was higher than that on the Ru/MgO catalyst. The Ru/MgAl2O4-1023 catalyst could be re-used for 3 times without significant lowering the yield of cyclohexene. Compared with the Ru/SBA-15-series catalysts, the catalyst stability was improved greatly, but the maximum yield of cyclohexene was lower. The different yield of cyclohexene is due to the different hydrophilic character of the support. Support with a hydrophilic character is more favorbale for the formation of cyclohexene, and the acid-base character of the support also has great influence on the formation of cyclohexene.The maximum yield of cyclohexene over Ru/MgAl2O4-series catalysts is lower than the expected in industry, meanwhile, numerous literatures and patents have showed that ZrO2 is an excellent catalyst support and dispersant in the liquid phase hydrogenation of benzene. In order to obtain higher yield of cyclohexene, the promoter is needed to modify the Ru catalyst, including Zn, Fe, Co, Ni, and rare earth elements etc. There are few reports about the promoting effect of noble metal element in the liquid phase hydrogenation of benzene. By choosing a suitable noble metal element (Pd, Pt), it is possible to form alloy with Ru, while the formation of alloy (RuPd) had shown better promoting effect in the hydrogenation of dimethylbenzene, nitrobenzene aromatic hydrocarbons.Thus, in this chapter, we use commercial ZrO2 as support and modify the Ru catalyst by Pd or Pt element to study the bimetallic effect in the liquid phase hydrogenation of benzene. The experimental results showed that the introduction of Pd or Pt could improve the catalytic activity and the yield of cyclohexene greatly. The maximum yield of cyclohexene increased from 38.5%(RuB/ZrO2) to 43.8%(RuPdB/ZrO2-0.2) and 44.2% (RuPtB/ZrO2-0.15), while the reaction time for the maximum yield of cyclohexene was shortened from 80 min (RuB/ZrO2) to 60 min (RuPdB/ZrO2-0.2) and 45 min (RuPtB/ZrO2-0.15). The improvement of the catalytic performance was due to the improvement of the dispersing degree, the thermal stability of the catalyst and the formation of surface alloy. Due to the low surface area of commercial ZrO2 (<10 m2·g-1), which restricts its application. There are many methods available to prepare ZrO2, resulting in different surface area, crystal structure and surface acid-base character of ZrO2. Herein, we prepared two kinds of ZrO2 (monoclinic and tetragonal) as supports for the RuB catalysts to study the effect of crystal structure and surface acid-base character on the partial hydrogenation of benzene. Py-IR characterization showed that monoclinic ZrO2 (ZrO2-M) had both Lewis acid site and Br(?)nsted acid site while tetragonal ZrO2 (ZrO2-T) had only Lewis acid sites. Under the same reaction conditions, by calcining the ZrO2-T and ZrO2-M materials at 873 K as supports to prepare supported catalysts and test their catalytic performance in the liquid phase hydrogenation of benzene, the maximum yield of cyclohexene was 46.6% (RuB/ZrO2-T-873) and 37.8%(RuB/ZrO2-M-873). The catalysts prepared by using ZrO2-T as support were more favorable for the formation of cyclohexene. By combining the experimental results and literature reports, benzene adsorbed on the Br(?)nsted acid site is more favorable for the formation of cyclohexane with the spill-over hydrogen from the metal active site, resulting in lower yield of cyclohexene. For the first time, we reported the influence of different acid site of the ZrO2 support in the liquid phase hydrogenation of benzene. The RuB/ZrO2-T-series catalysts may have excellent application in industry.更多还原