【作者】 陈红侠；

【导师】 范彬彬； 李瑞丰；

【作者基本信息】 太原理工大学 ， 化学工程， 2009， 硕士

【摘要】 在催化氧化过程中,烯烃的氧化是使碳氢化合物转化成含氧化合物的一类重要反应。环己烯的环氧化是烯烃环氧化的一个探针反应,具有很典型的代表性。环己烯氧化包括双键的氧化和烯丙位的α-H氧化,其中双键环氧化生成的环氧环己烷以及烯丙位氧化生成的环己烯醇和环己烯酮都是重要的有机化工原料和中间体,广泛应用于石油、医药、农药、饲料、高分子材料、食品、染料、纺织、溶剂和精细化工产品等众多领域。本文通过利用洁净易得的氧化剂-分子氧,以环己烯的催化氧化作为研究对象,在不加入共还原剂的条件下考察了不同方法,不同条件下制备的非均相锰氧化物催化剂和MnxOy/SiO2催化剂的催化性能,并且通过多种物化手段对其进行了表征。一、锰氧化物催化剂的制备及其在氧气氧化环己烯反应中的催化性能(1)采用沉淀法和焙烧法(分别以MnCO3和γ-MnOOH为前驱物)制备了Mn3O4催化剂,并对其在环己烯氧化反应中的催化性能进行了考察。结果表明不同方法所制备的催化剂表现出了不同的催化性能,其中,采用沉淀法制备的Mn3O4催化剂催化性能最佳,并且在最佳的反应条件下,环氧环己烷、环己烯醇和环己烯酮的总收率可达42.1%,其中环氧环己烷的收率达到16.2%。(2)考察了沉淀法制备Mn3O4催化剂过程中,pH值对所制催化剂的物化性能和催化性能的影响。结果表明,催化剂的比表面随pH值升高而增大,然而环氧环己烷、环己烯醇和环己烯酮的总收率却有所降低,但对环氧环己烷的收率影响不大。综合考虑,在相同反应条件下,于pH值为9时制备的Mn3O4催化剂在环己烯反应中具有最高的催化性能。(3)以pH值为9时制备的Mn3O4为催化剂,考察了焙烧温度、溶剂、反应温度、反应时间和催化剂用量等反应条件对Mn3O4催化性能的影响。溶剂种类对环己烯双键氧化和烯丙位氧化的选择性影响较大,1,2,4,5-四甲基苯为溶剂时Mn3O4催化剂的催化性能最佳。为了进一步解释这一结果,对反应机理作了初步的考察,其遵循自由基机理,且发现溶剂1,2,4,5-四甲基苯参与了反应。GC-MS分析显示在Mn3O4催化剂作用下,1,2,4,5-四甲基苯生成了2,4,5-三甲基苯甲醛,相当于共还原剂,有助于环氧环己烷的生成。二、MnxOy/SiO2催化剂的制备及其在氧气氧化环己烯反应中的催化性能(1)采用共沉淀法、浸渍法和溶胶-凝胶法制备了MnxOy/SiO2催化剂,并对其在环己烯氧化反应中的催化性能进行了考察。结果表明不同方法所制备的MnxOy/SiO2催化剂表现出了不同的催化性能。其中,采用溶胶-凝胶法制备的MnxOy/SiO2催化剂催化性能最佳,且在最佳反应条件下,环氧环己烷、环己烯醇和环己烯酮的总收率可达35.1%,环己烯酮的收率达到25.7%。(2)在采用溶胶-凝胶法制备MnxOy/SiO2的过程中,制备参数是影响催化剂催化性能的主要因素,其中制备过程中pH值是影响催化剂性能的关键因素。于pH值为2-9的范围内制备了系列MnxOy/SiO2催化剂,详细考察了在制备过程中pH值对所制MnxOy/SiO2催化剂的物化性能和催化性能的影响。结果表明不同pH值不仅使催化剂具有不同比表面、金属负载量,而且还使所制备的催化剂的催化氧化性能存在巨大差异。在相同反应条件下,于pH值为4.7时制备的MnxOy/SiO2在环己烯反应中具有最高的反应活性。(3)以pH值为4.7时制备的MnxOy/SiO2为催化剂,考察了反应温度、反应时间、溶剂种类及用量和焙烧温度等条件对MnxOy/SiO2催化性能的影响,优化了反应条件。更多还原

【Abstract】 Epoxidation of alkenes can be regarded as one kind of important reactions which can convert hydrocarbons into oxygen-containing compounds. The epoxidation of cyclohexanol is a typical example. It consists of epoxidation of double bond, producing epoxycyclohexane, and ofα-H allyl oxidation, forming 2-cyclohexene-1-ol and 2-cyclohexene-1-one. Both of these products, as important organic chemical raw materials and intermediates, are widely used in the petrochemical, medicine, pharmaceutical, animal feed, polymer materials, foodstuffs, dyes, textiles, fine chemicals and solvents. In this thesis, a series of manganese oxide and MnxOy/SiO2 catalysts were prepared under different conditions in different ways and characterized by a variety of physico-chemical techniques. Further, their catalytic properties for the epoxidation of cyclohexene with oxygen were investigated.Ⅰ) Preparation of manganese oxide catalysts and their catalytic properties in the oxidation of cyclohexene.(1) Mn3O4 catalyst was prepared by precipitation of aqueous Mn salt solutions and calcinations (using MnCO3 andγ-MnOOH precursors, respectively). Catalytic tests show that the samples prepared in different ways exhibited different performances. The catalysts prepared by the precipitation method showed better catalytic performance. Under the optimum reaction conditions, the sum yields of epoxycyclohexane, 2-cyclohexene-1-ol and 2-cyclohexene-1-one reached 42.1%, and yield of epoxycyclohexane reached 16.2%, respectively.(2) The effect of the pH value in the precipitation mixture on the physicochemical properties and catalytic performance of Mn3O4 was investigated. It has been shown that the samples prepared at different pH values had different surface areas. Although the sum yields of epoxycyclohexane, 2-cyclohexene-1-ol and 2-cyclohexene-1-one decreased with increasing pH values, the epoxycyclohexane yield was not significantly changed. The catalyst prepared at pH=9 were highly active for the epoxidation of cyclohexene.(3) The influence of reaction conditions, including calcination temperature, solvent, amount of catalyst, reaction time and reaction temperature, on the catalytic properties was investigated by using the catalyst prepared at pH=9 as an example. It was found that the preferential oxidation of double bond orα-H allyl oxidation was dependent on the solvents employed, and 1,2,4,5-tetramethylbenzene gave the highest the sum yields of epoxycyclohexane, 2-cyclohexene-1-ol and 2-cyclohexene-1-one and yield of epoxycyclohexane. In order to interpret such a result, the catalytic mechanism was further studied. It was shown that the reaction occurred via a radical mechanism, and the solvent took part in the reaction. GC-MS analysis shows that oxidation of 1,2,4,5-tetramethylbenzene occurred, producing 2,4,5- trimethylbenzaldehyde, which acted as a co-reductant in the epoxidation of cyclohexene.Ⅱ) Preparation of manganese-based oxide catalysts and their catalytic properties in the oxidation of cyclohexene.(1) The MnxOy/SiO2 catalysts were prepared by the co-precipitation method, the impregnation method and the sol-gel method. An extensive evaluation shows that the catalytic properties of MnxOy/SiO2 catalysts for the oxidation of cyclohexene depended on the preparation methods. The MnxOy/SiO2 sample prepared by the sol-gel method exhibited the highest activity. When the reaction was carried out at the optimum reaction conditions, the sum yields of epoxycyclohexane, 2-cyclohexene-1-ol and 2-cyclohexene-1-one reached 35.1%, and 2-cyclohexen-1-one reached 25.7%, respectively.(2) Preparation conditions markedly affected the catalytic properties when the sol-gel method was used to prepare the MnxOy/SiO2 catalysts. It was found that the pH value is a key factor determining the catalytic performance. The MnxOy/SiO2 catalysts prepared at different pH values in the range of 2-9, not only had different surface areas and metal loadings, but also exhibited remarkably different catalytic properties. The sample prepared at pH values of 4.7 gave the highest conversion in the oxidation of cyclohexene.(3) The effect of reactions conditions, including reaction temperature, reaction time, the type and amount of solvent and catalyst calcination temperature, on the catalytic properties of MnxOy/SiO2 prepared at pH=4.7 were investigated. The optimum reaction conditions were obtained.更多还原