膨胀石墨负载CuO_x催化剂的制备及其对分子氧氧化环己烯催化性能研究

【作者】 张瑞荣；

【导师】 唐瑞仁；

【作者基本信息】 中南大学 ， 有机化学， 2011， 硕士

【摘要】 烯丙位氧化反应是一类十分重要的有机氧化反应,环己烯在烯丙位发生氧化可以生成2-环己烯-1-酮,2-环己烯-1-醇等重要的化工中间体。其传统生产工艺是采用铬酸氧化环己烯制取,存在产率低、分离困难,且污染严重等问题。分子氧易得廉价,对环境无污染,是氧化反应最理想的氧源,但由于分子氧的相对化学惰性,氧化效率低,因此,寻找高活性、高选择性的催化剂是实现环己烯选择性氧化制备环己烯酮的关键。本文从催化剂制备及环己烯氧化产物的合成方法出发,主要开展了以下几个方面的工作：(1)通过还原法制备了鳞片石墨(FG)负载CuOx催化剂(Cu/FG),考察其催化分子氧氧化环己烯性能。结果表明主要发生烯丙位氧化生成2-环己烯-1-酮和2-环己烯-1-醇。考察了反应条件对环己烯选择性氧化反应的影响：在溶剂乙腈中,以分子氧为氧化剂,H202为引发剂,在60℃反应12 h,其催化效果最佳。GC-MS检测显示反应转化率为45.8%,烯丙位氧化产物的总选择性可达90%以上,其中2-环己烯-1-酮的选择性可达49.7%。(2)FG经化学氧化处理,高温膨胀后,得到蠕虫状膨胀石墨(EG),制备了膨胀石墨负载纳米CuOx催化剂(Cu/EG),考察其催化分子氧氧化环己烯性能,结果显示Cu/EG的催化效果明显优于Cu/FG:在较温和的条件下可以有效的催化分子氧氧化环己烯反应,环己烯的转化率达到70%以上,2-环己烯-1-酮的选择性可达61.8%。通过SEM及其对应的EDAX、XRD、FT-IR、ICP和N2吸附脱附等方法对催化剂及其载体进行表征,结果表明,FG进行化学氧化高温膨胀处理,一方面增大了载体的比表面积,在EG表面形成了-OH,C=O和C-O-C等官能团；另一方面还引入了Fe和Mn,提供了多元催化活性中心,提高了其催化能力。(3)采用间歇式加料法,制备了具有十字针状特殊形貌的膨胀石墨负载纳米CuOx催化剂(Cu/EG),其化学组成与一次加料还原法制备的Cu/EG完全相同。但催化效果却有一定程度的提升：环己烯转化率达到90%以上,烯酮产物选择性并没有明显的上升。考察了催化剂负载量、溶剂、制备方法和反应时间等因素对反应的影响,优化了反应工艺。在最优条件下,环己烯的转化率达到98.2%,烯酮产物的选择性为62.1%。该类催化剂可以重复使用3次,催化效果没有明显下降。进一步探讨了铜催化剂在此体系中可能的反应机理。(4)通过改变强氧化剂KMnO4(?)插层剂FeCl3的用量,制备了三种不同类型的膨胀石墨：EG1、EG2和EG3。间歇式加料硼氢化钠还原法制备了铜负载量接近的三类催化剂：Cu/EG1, Cu/EG2和Cu/EG3。在相同的反应条件下催化分子氧氧化环己烯反应。结果表明, Cu/EG3表现出较好的催化效果：环己烯的转化率达到98.9%,烯酮产物的选择性达到71.3%。对Cu/EG3掺杂Bi, Co, Ni,对该类催化剂的催化效果有一定的影响。其中Bi掺杂的效果最好：环己烯的转化率达到100%,烯酮产物的选择性达到78.9%。此催化剂循环使用4次后催化性能仍然良好,反应的转化率和烯酮产物的选择性仍可达88.3%,73.2%。更多还原

【Abstract】 2-cyclohexene-l-one and its derivatives are very important Chemical intermediates in the manufacture of high-value fine chemicals, agrochemicals and pharmaceuticals. In traditional production process, 2-cyclohexene-1-one is prepared by oxidation of cyclohexene with chromic acid. There are many problems concerning low yield, catalyst lost, harsh condition, and serious pollution. Consequently, the development of oxidation reaction using molecular oxygen as a cheap, environmentally clean and convenient oxidant has attracted significant attention. Unfortunately, it was observed that the oxidation efficiency of molecular oxygen was poorer than other oxidants. Therefore, it is the key challenge to find effective catalysts for activation of molecular oxygen in developing new procedures using O2 as a green oxidant. Herein, with the aim to developing novel and more efficient catalyst, the research works below have been done:(1) Flake graphite supported CuOx catalyst (Cu/FG) is prepared and characterized by SEM, TEM and XRD, and applied to the oxidation of cyclohexene with molecular oxygen.2-cyclohexene-1-one and 2-cyclohexene-ol are got as the main products by ally lic oxidation. The influence of a series of different conditions for the reaction is also investigated. To a solution of cyclohexene (0.02 mol) in acetone (20 mL) in a three-necked flask equipped reflux condenser was added Cu/FG(1 wt%based on cyclohexene), the mixture was heated to 60℃and stirred for 12 h under 1 atm O2. The reaction conversion rate is 45.8%, and the total selectivity of allylic oxidation products is more than 90%, in particular, the selectivity of 2-cyclohexene-1-one could reach 49.7%.(2) Expanded graphite (EG) is prepared from FG by chemical oxidation. EG supported CuOx nano-catalysts (Cu/EG) is prepared and applied to the oxidation of cyclohexene reaction. Cu/EG shows superior catalytic activity to Cu/FG. The conversion of cyclohexene can be over 70%, the selectivity of 2-cyclohexene-l-one can be reached 61.8%. Furthermore, in order to explore the reasons, the catalysts are characterized by SEM and the corresponding EDAX, XRD, FT-IR, ICP and N2 adsorption and desorption, etc. Experimental results show the surface area of carriers can be increased by the chemical oxidation, and EG formed-OH, C=O, C-O-C and other functional groups on the surface; Meanwhile, Fe and Mn elements are also introduced into EG, which increase the multiple catalytic active center.(3) A novel cross-shaped Cu/EG is prepared by intermittent feeding method. This kind of catalyst showed better catalytic activity:conversion of cyclohexene can be more the 90%. In the optimum conditions, the conversion and the selectivity of 2-cyclohexene-l-one are 98.2% and 62.1%respectively. Such catalysts can be reused 3 times with high activity. Based on the experimental results and the literatures, the possible reaction mechanism is proposed.(4) EG1, EG2 and EG3 are prepared by changing the amount of FeCl3 and KMnO4 in the chemical oxidation. Then Cu/EG1, Cu/EG2 and Cu/EG3 are prepared by intermittent feeding. Cu/EG3 shows the best catalytic effect:the conversion of cyclohexene is 98.9%, and the selectivity of 2-cyclohexene-l-one is 71.3%. Furthermore, Bi, Co and Ni are doped into Cu/EG3 respectively. Among these catalysts, Bi-doping Cu/EG3 shows the best catalytic activity:the conversion of cyclohexene is 100%, and the selectivity of 2-cyclohexene-l-one is 78.9%. The supported catalyst can be reused for 4 times with high conversion (88.3%) and selectivity (73.2%).更多还原