高等学校化学学报

高等学校化学学报 ›› 2002, Vol. 23 ›› Issue (10): 1952.

• 研究论文 • 上一篇    下一篇

氟化γ-Al2O3表面酸性的NMR和FTIR表征

刘常坤1, 叶朝辉2   

  1. 1. 中山学院应用化学系, 中山 528403;
    2. 中国科学院武汉物理与数学研究所, 波谱与原子分子物理国家重点实验室, 武汉 430071
  • 收稿日期:2001-08-23 出版日期:2002-10-24 发布日期:2002-10-24
  • 通讯作者: 刘常坤(1958年出生),男,博士,教授,主要从事催化研究.E-mail:maxm ax@stinfo.net E-mail:maxmax@stinfo.net
  • 基金资助:

    中国科学院武汉物理与数学研究所波谱与原子分子物理国家重点实验室基金资助

NMR and FTIR Characterization of Surface Acidity of Fluorinated γ-Asl2O3

LIU Chang-Kun1, YIE Zhao-Hui2   

  1. 1. Department of Applied Chemistry, Zhongshan College, Zhongshan 528402, China;
    2. Wuhan Institute of Physics and Mathematic, State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Chinese Academy of Sciences, Wuhan 430072, China
  • Received:2001-08-23 Online:2002-10-24 Published:2002-10-24

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摘要： 用红外光谱和核磁共振技术研究了氟化作用对γ-Al2O3的表面酸性(酸中心类型、强度及数量)的影响.吡啶和二甲基吡啶在氟化γ-Al2O3(F/γ-Al2O3)表面上吸-脱附的IR光谱和三甲基膦在F/γ-Al2O3表面上吸附的31PMASNMR结果表明,F/γ-Al2O3表面上既存在Lewis酸位又存在Bronsted酸位.L酸的总量随氟含量的增加而减少,但其强度随之增加,且同时产生几种新的L酸位.B酸的数量和强度在样品含氟量为2%～3%间存在极大值.研究还表明,三甲基膦是一种测量F/γ-Al2O3表面酸性的灵敏的NMR探针分子,31PMASNMR和红外光谱的测试结果基本一致.同时,对氟化过程中酸位形成和变化机理进行了探讨.

关键词: 氟化&gamma, -Al2O3, 表面酸性, 吸附, 固体NMR, InsituFTIR

Abstract: The effect of fluorination on the surface acidity of γ-Al2O3 and the influence of the amount of fluorine on the types strength and number of acid sites have been studied. IR spectra of pyridine(PY) and 2,6-dimethylpyridine(DMPY) adsorbed-desorbed on fluorinated γ-Al2O3(F/γ-Al2O3) and 31P MAS NMR of trimethylphosphine(TMP) adsorbed on F/γ-Al2O3 have been used to measure the acidities of F/γ-Al2O3 . It has been found that F/γ-Al2O3 presents both Brnsted and Lewis sites. IR spectra of pyridine adsorbed on F/γ-Al2O3 pretreated in vacuum at 300 K show four bands at 1 451, 1 491, 1 580 and 1 617 cm-1, the bands are assigned to PY adsorbed on Lewis acid sites, and two bands at 1 544 and 1 640 cm-1 are assigned to PY adsorbed on Bronsted acid sites. IR spectra of 2,6-dimethylpyridine adsorbed on F/γ-Al2O3 pretreated in vacuum at 300 K shows a major band at 1 637 cm-1 due to DMPY adsorbed on Bronsted acid sites. 31P MAS NMR spectra of trimethylphosphine adsorbed on F/γ-Al2O3 pretreated in vacuum at 353 K show three peaks at δ -56 5, -28 2 and -21 9 are assigned to TMP chemisorption to different types of Lewis sites, and a peak at δ -2 8 is assigned to TMP chemisorption to Bronsted acid site. When the fluorine content increases, the total number of Lewis acid sites decreases, whereas their strength increases, a few of new types of Lewis acid sites are created simultaneously. The number and strength of Brnsted acid site presents a maximum for samples with 2%-3% of fluorine content. TMP as a sensitive NMR probe molecule is introduced for acidity measurements on F/γ-Al2O3 surfaces in the present study. 31P MAS NMR results agree with that of IR.

Key words: Fluorinated γ-Al2O3, Surface acidity, Adsorption, Solid NMR, In situ FTIR

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