Full-Text Search:
Home|Journal Papers|About CNKI|User Service|FAQ|Contact Us|中文
《Chemical Research In Chinese Universities》 2002-10
Add to Favorite Get Latest Update

NMR and FTIR Characterization of Surface Acidity of Fluorinated γ-Asl_2O_3

LIU Chang-Kun 1*, YIE Zhao-Hui 2 (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 A  
The effect of fluorination on the surface acidity of γ-Al 2O 3 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-Al 2O 3(F/γ-Al 2O 3) and 31P MAS NMR of trimethylphosphine(TMP) adsorbed on F/γ-Al 2O 3 have been used to measure the acidities of F/γ-Al 2O 3 . It has been found that F/γ-Al 2O 3 presents both Brnsted and Lewis sites. IR spectra of pyridine adsorbed on F/γ-Al 2O 3 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-Al 2O 3 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-Al 2O 3 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-Al 2O 3 surfaces in the present study. 31P MAS NMR results agree with that of IR.
【Fund】: 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
【CateGory Index】: O643.3
Download(CAJ format) Download(PDF format)
CAJViewer7.0 supports all the CNKI file formats; AdobeReader only supports the PDF format.
©2006 Tsinghua Tongfang Knowledge Network Technology Co., Ltd.(Beijing)(TTKN) All rights reserved