物理化学学报 >> 1988, Vol. 4 >> Issue (03): 301-306.doi: 10.3866/PKU.WHXB19880315

研究论文 上一篇    下一篇

红外光谱法考察苯加氢过程中的氢溢流效应

董庆年; 单雅枫; 肖有燮; 杨立新; 钟炳   

  1. 中国科学院山西煤炭化学研究所
  • 收稿日期:1986-09-09 修回日期:1987-07-25 发布日期:1988-06-15
  • 通讯作者: 董庆年

FTIR STUDY ON HYDROGEN SPILLOVER IN THE BENZENE HYDROGENATION SYSTEM

Dong Qingnian*; Shan Yafeng; Xiao Youxie; Yang Lixin; Zhong Bin   

  1. Shanxi Institute of Coal Chemistry; Academia Sinica; Taiyuan
  • Received:1986-09-09 Revised:1987-07-25 Published:1988-06-15
  • Contact: Dong Qingnian

摘要: 以点状Pt/η-Al_2O_3催化剂作为产生溢流氢的“源”, 用原位红外光谱观察η-Al_2O_3上苯的加氢过程, 发现溢流氢在η-Al_2O_3表面上可以迁移相当长的距离, 它的迁移速度是苯加氢反应的控制步骤。结合TPSR-MS数据, 认为苯的加氢是分步进行的, 它先被加氢成环已二烯, 再转化成环已烯, 最终形成环已烷脱附。这些反应都是快速反应。

Abstract: Hydrogen spillover has been studied by means of benzene hydrogenation reaction on Al_2O_3. The spillover hydrogen is produced from a point source of spillover Pt/Al_2O_3. Observing benzene adsorbed on Al_2O_3 by in situ FTIR, it is found that the adsorption is a physisorption which occurs by intereaction between π electrons of benzene and surface OH groups of Al_2O_3. The adsorbed force existing between benzene and OH groups is weak, and can not make adsorbed benzene being in active state. Therefore, the benzene hydrogenation reaction on Al_2O3 containing a point source of spillover Pt/Al_2O3 is mainly an interface reaction.
The infrared spectra following observation benzene hydrogenation reaction illustrate that there are a few cyclohexane molecules in beam after the reaction proceeds for 15 mimutes at 50 ℃ and 550 Torr of H_2, and its intensities of CH_2 stretching vibration bands increase linearly with time until all benzene molecules in beam are transformed after 5 hours. These data imply that the spillover hydrogen may migrate some distance on Al_2O3 surface under experiment conditions, and its migrate velocity is the rate controlling step for benzene hydrogenation.
Cyclohexadiene and cyclohexene are observed in further temperature progra mmed surface reaction-mass spectroscopy (TPSR-MS) on Pt/Al_2O_3 catalyst. The result clearly reveals that some successive steps are involved in the hydrogenation process, i.e., firstly benzene is hydrogenated into cyclohexadiene, and then it is transformed into cyclohexene, finally cyclohexane is formed and desorbed In view of their examinable concentrations are low, it may be considered that all these steps are fast.