物理化学学报 >> 2013, Vol. 29 >> Issue (03): 597-604.doi: 10.3866/PKU.WHXB201301041

催化和表面科学 上一篇    下一篇

γ-MnO2的形貌控制及其甲苯液相氧化性能

林健, 蔡钒, 张国玉, 杨乐夫, 杨金玉, 方维平   

  1. 厦门大学化学化工学院, 醇醚酯清洁生产国家工程实验室, 厦门 361005
  • 收稿日期:2012-09-20 修回日期:2013-01-02 发布日期:2013-02-25
  • 通讯作者: 杨乐夫, 方维平 E-mail:lfyang@xmu.edu.cn; wpfang@xmu.edu.cn
  • 基金资助:

    国家重点基础研究发展规划项目(973) (2010CB226903)资助

Preparation of Morphology-Tuned γ-MnO2 and Catalytic Performance for the Liquid-Phase Oxidation of Toluene

LIN Jian, CAI Fan, ZHANG Guo-Yu, YANG Le-Fu, YANG Jin-Yu, FANG Wei-Ping   

  1. College of Chemistry and Chemical Engineering, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ether, Esters, Xiamen University, Xiamen 361005, P. R. China
  • Received:2012-09-20 Revised:2013-01-02 Published:2013-02-25
  • Supported by:

    The project was supported by the National Key Basic Research Program of China (973) (2010CB226903).

摘要:

通过在回流法制备流程中引入CTAB(十六烷基三甲基溴化铵)、PEG6000(聚乙二醇6000)及P123(聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物)等表面活性剂对γ-MnO2催化剂进行形貌控制, 同时采用X射线衍射(XRD)、扫描电镜(SEM)、N2吸附(BET)、热重分析(TGA)、O2程序升温脱附(O2-TPD)以及H2程序升温还原(H2-TPR)等技术对不同形貌γ-MnO2的结构、氧脱附及还原性能进行表征, 并考察了其在常压和无溶剂条件下甲苯选择性氧化反应体系的催化特性. 同时, 对于陈化时间对形貌的影响作用进行了考察. 结果表明: 不同形貌的γ-MnO2的氧化还原特征及催化活性存在显著差异, 其中在经PEG6000进行修饰的γ-MnO2中含有较多的阴离子空位及混合价态, 因此有助于分子氧在表面的活化, 具有较高的表面比活性; 而经P123进行表面修饰的γ-MnO2成晶结构规整、比表面积大, 对甲苯液相直接氧化反应则表现出最佳的质量比活性, 甲苯转化率达18.1%, 含氧化合物总选择性为87.4%, 其中苯甲酸的选择性达到73.2%.

关键词: γ-MnO2, 甲苯选择性氧化, 形貌控制, 氧物种, 表面活性剂

Abstract:

Introducing surfactants including hexadecyltrimethylammonium bromide (CTAB), macrogol 6000 (PEG6000), and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) triblock copolymer (P123) into the refluxing aqueous crystal nucleus slurry yielded morphology-tuned microcrystalline γ-MnO2. γ-MnO2 and the influence of surfactant modification were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption (BET), thermogravimetry analysis (TGA), O2 temperature programmed desorption (O2-TPD), and temperature programmed H2 reduction (H2-TPR). Surfactants led to differences in γ-MnO2 morphology, surface area, oxygen desorption behavior and reducibility. The effect of reflux time on catalyst morphology is discussed. The catalytic performance of γ-MnO2 during the solvent-free atmospheric oxidation of toluene was evaluated. PEG6000 modified γ-MnO2 exhibited the highest catalytic activity judging by surface area because of a greater mixed valency and more anion vacancies. The greatest mass specific activity was obtained for P123 modified γ-MnO2 with the largest surface area. Optimized reaction conditions yielded an 18.1% toluene conversion, and 87.4 and 73.2% total selectivity and selectivity for benzoic acid, respectively.

Key words: γ-MnO2, Selective oxidation of toluene, Morphology tuning, Oxygen species, Surfactant

MSC2000: 

  • O643