苯选择加氢制环己烯新型Ru-Zn催化剂的研究

【作者】 黄振旭；

【导师】 刘寿长；

【作者基本信息】 郑州大学 ， 物理化学， 2006， 硕士

【摘要】 苯选择加氢制环己烯具有原子经济性和环境友好等特点，开展苯选择加氢制环己烯催化剂的研究具有重要的应用价值和一定的学术意义。本论文主要工作是：研究了新型Ru-Zn催化剂的制备方法，并对催化剂进行了表征。主要结论如下： 一、催化剂的制备和操作条件研究：研究了各种因素对沉淀法制备的Ru-Zn催化剂活性选择性的影响，和Fe／Ru比对Ru-Fe催化剂的影响。确定了Ru-Zn和Ru-Fe催化剂的最佳制备条件为：Zn／Ru或Fe／Ru质量比8:92，RuCl₃·xH₂O的浓度为0.18mol·L^-1，在70～80℃温度下，将RuCl₃和ZnSO₄·7H₂O或FeSO₄·6H₂O的混合溶液，采用反加法缓慢滴加到过量25％的NaOH溶液中，得到黑色胶状沉淀，继续搅拌10分钟，陈化24h，将沉淀及上清液一并转移至高压釜中。在150℃，5.0MPa，1000r／min还原2h。冷却后取出放置24h，将沉淀洗涤至pH=8±0.5。 催化剂的加氢条件：反应浆液由水、苯、ZnSO₄、催化剂和ZrO₂组成。50mL H₂O，29mL C₆H₆，0.25g Ru-Zn或Ru-Fe催化剂，8.79g ZnSO₄·7H₂O、1.25g ZrO₂。预处理1h。反应条件：150℃，5.0MPa氢气压力，搅拌速率1000r／min。 在上述条件下，在Ru-Zn催化剂上，15min时，苯转化率77.3％，环己烯选择性63.5％，收率49.1％，优于文献报道结果。 二、催化剂的表征。对催化剂进行了活性选择性测定，利用X射线衍射、物理吸附仪，激光粒度分析仪，化学吸附仪等对催化剂进行了表征。XRD给出了Ru-Zn催化剂的晶体和固溶体特征。当Zn／Ru比小于12％时，Ru和Zn以固溶体形式存在；当Zn／Ru比大于15％时，Ru-Zn催化剂体相中观察到零价锌。并从溢流现象和化学反应耦合的观点解释了这一实验事实。XRD半高宽法给出，随着Zn含量的增加，Ru微晶粒径由5.6nm变为4.6nm。BET比表面数据表明，纯Ru催化剂的比表面积(222m²·g^-1)比含Zn催化剂(～72m²·g^-1)大得多。催化剂上述物性参数的变化是助剂对催化剂活性选择性的影响的原因之一。更多还原

【Abstract】 The preparation and characterization of a novel Ru-Zn catalyst for selective hydrogenation of benzene to cyclohexene have been carried out in this paper. The selective hydrogenation of benzene is of great synthetic and industrial line owing to its atomic economy and clean production; therefore it is very significant to study on these catalysts no matter in industrial application or in theory field.1 .The preparation conditions of Ru-Zn and Ru-Fe catalyst are as following: The suitable mass ratio of Zn/Ru is 8:92, and the concentration of RuCl₃· xH₂O is about 0.18 mol·L^-1. At 70⁸0℃, the mixture of RuCl₃· xH₂O and ZnSO₄ was added drop by drop to a solution of sodium hydroxide （20 wt.% NaOH）, leading to a black ruthenium-zinc hydroxide precipitate. Then the precipitate together with the mother liquid was reduced in an autoclave under the conditions of 140℃, hydrogen pressure keeps 5.0 MPa and stirring rate of 1000 r/min for 2h. After reduction, the precipitate was washed thoroughly to pH=8±0.5 .The optimal operation conditions of the Ru-Zn catalyst are that the reaction temperature is about 140℃, the hydrogen pressure is 5.0 MPa and the stirring rate is 1000 r/min, pretreatment time is 1 h. The suitable composition of the slurry is 50mL H₂O, 29mL C₆H₆, 0.25 g Ru-Zn or Ru-Fe catalyst, 8.79g ZnSO₄-7H₂O and 1.25g ZrO₂.The Ru-Zn catalyst was used for hydrogenation of benzene under above conditions, at 15 min, the yield of cyclohexene achieve 49.1% at benzene conversion of 77.3%.2. XRD results show crystal and solid solution character of the catalysts. Zinc exists in its metal state in the catalyst with lower content of zinc, while the content of zinc increasing further, a new phase of zinc is found. Meanwhile it was found that Ru crystallite size decreases from 5.6 nm to 4.6 nm with increase of the content of zinc in the catalyst.BET results show that activities of the catalysts are relative to their specific surface areas. The larger the specific surface area is, the higher the activity and更多还原