物理化学学报 >> 2010, Vol. 26 >> Issue (02): 338-344.doi: 10.3866/PKU.WHXB20100208

催化和表面结构 上一篇    下一篇

水热处理对纳米HZSM-5分子筛酸性及催化甲醇制丙烯反应性能的影响

毛东森, 郭强胜, 孟涛, 卢冠忠   

  1. 上海应用技术学院化学与环境工程学院应用催化研究所, 上海 200235
  • 收稿日期:2009-10-13 修回日期:2009-11-13 发布日期:2010-01-26
  • 通讯作者: 毛东森 E-mail:dsmao@sit.edu.cn; dsmao1106@yahoo.com.cn

Effect of Hydrothermal Treatment on the Acidity and Catalytic Performance of Nanosized HZSM-5 Zeolites for the Conversion of Methanol to Propene

MAO Dong-Sen, GUO Qiang-Sheng, MENG Tao, LU Guan-Zhong   

  1. Research Institute of Applied Catalysis, School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 200235, P. R. China
  • Received:2009-10-13 Revised:2009-11-13 Published:2010-01-26
  • Contact: MAO Dong-Sen E-mail:dsmao@sit.edu.cn; dsmao1106@yahoo.com.cn

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摘要：

对纳米HZSM-5分子筛进行水热处理, 利用N2吸附-脱附、X射线衍射(XRD)、铝固体核磁共振(27Al MAS NMR)、氨-程序升温脱附(NH3-TPD)和吡啶吸附傅立叶变换红外(FT-IR)光谱等技术对改性前后样品的结构和酸性进行了详细表征, 并在常压、500 ℃和甲醇质量空速(WHSV)为1.0 h-1的反应条件下, 在连续流动微型固定床反应器上考察了其催化甲醇转化制丙烯反应的性能. 结果表明, 适度的水热处理使纳米HZSM-5分子筛骨架脱铝并经柠檬酸洗涤而除去, 酸量减少, 酸强度降低, 孔容和孔径增大, 从而使丙烯的选择性和维持甲醇完全转化的反应时间(即催化剂寿命)分别由改性前的30.1%和75 h显著提高至38.9%和160 h. 但过高温度的水热处理使纳米HZSM-5分子筛的酸性明显减弱, 强酸中心几乎完全消失, 故使丙烯的选择性和催化剂的稳定性反而大大降低.

关键词: 水热处理, 纳米HZSM-5分子筛, 甲醇, 丙烯, 选择性, 稳定性

Abstract:

A series of modified nanosized HZSM-5 zeolites were prepared by hydrothermal treatment at different temperatures and characterized by the adsorption and desorption of N2, X-ray diffraction (XRD), Al solid state magic angle spinning nuclear magnetic resonance (27Al MAS NMR), temperature-programmed desorption of ammonia (NH3-TPD), and Fourier transforminfrared (FT-IR) spectroscopy of adsorbed pyridine techniques. The conversion of methanol to propene was tested using a continuous flow fixed-bed microreactor at atmospheric pressure, 500 ℃, and a methanol weight hourly space velocity (WHSV) of 1.0 h-1. Results showed that after the appropriate hydrothermal treatment, some of Al was removed from the framework of zeolite and extracted out of the zeolite channels after treatment with an aqueous solution of citric acid. This led to a decrease in the strength and amount of acidic sites and an increase in the volume and diameter of the pores. As a result, propene selectivity and the reaction time continued to maintain the total conversion of methanol (i.e., life time of catalyst) increased significantly to 38.9%and 160 h from 30.1%and 75 h over the parent nanosized HZSM-5 zeolite. However, severe hydrothermal treatment decreased the acidity remarkably and the strongly acidic sites were almost totally destroyed, resulting in a remarkable decrease both in propene selectivity and catalyst stability.

Key words: Hydrothermal treatment, Nanosized HZSM-5 zeolite, Methanol, Propene, Selectivity, Stability