Solid-state NMR investigation of acid sites in dealuminated HZSM-5 zeolite

	Solid-state NMR investigation of acid sites in dealuminated HZSM-5 zeolite
	Ye, CH; Deng, F; Du, YR
刊名	MAGNETIC RESONANCE IMAGING
	1996
卷号	14 期号:7-8 页码:945-946
ISSN号	0730-725X
文献子类	Article
英文摘要	The acid sites and the hydration behaviors of dealuminated HZSM-5 zeolites (calcined at 550, 600, 650, and 700 degrees C) were characterized by high-resolution H-1 MAS, H-1{(27)A1} spin-echo double resonance in combination with (27)A1 MAS NMR, Apart from the usually observed peaks for dealuminated zeolite HZSM-5, a narrow plus a broad peak simultaneously appears at ca.6.9 ppm in the H-1 spectra and they exhibit different decay behavior in the H-1{(27)A1}) double-resonance experiments, The existence of the former signal indicates that Lewis acid sites may be formed in the zeolites after calcination, By means of the spin echo double resonance technique, we observed for the first time a previously unexpected narrow signal at 5.2 ppm, which resonates on the downfield side of Bronsted acid signal (4.3 ppm) and cannot he resolved in the 1H MAS spectra, This new signal is probably due to another kind of Bronsted acid site, locating in the small cages bounded by four- and five-membered rings, Three narrow peaks at 50 ppm, 30 ppm, and 0 ppm are superimposed on a very broad signal in the (27)A1 MAS NMR spectra of dried HZSM-5. The intensity of the line at 50 ppm is significantly reduced compared with that of the rehydrated sample, (27)A1 MAS NMR suggests that most part of the four-coordinated framework Al turns into a intermediate case between four-and three-coordinated A1 after the dehydration and this process is reversible upon dehydration/rehydration, While some framework A1 atoms are transformed into three-coordinated A1 species and Lewis acid sites are, thus, generated in the dealuminated zeolites, For the signal at 30 ppm, the hydration leads to a dispersion in the chemical shift or the quadrupole interaction, which broadens its linewidth in hydrated samples. Copyright (C) 1996 Elsevier Science Inc.
WOS研究方向	Radiology, Nuclear Medicine & Medical Imaging
语种	英语
出版者	PERGAMON-ELSEVIER SCIENCE LTD
WOS记录号	WOS:A1996VW49700050
内容类型	期刊论文
源URL	[http://ir.wipm.ac.cn/handle/112942/12649]
专题	中国科学院武汉物理与数学研究所
通讯作者	Deng, F
推荐引用方式 GB/T 7714	Ye, CH,Deng, F,Du, YR. Solid-state NMR investigation of acid sites in dealuminated HZSM-5 zeolite[J]. MAGNETIC RESONANCE IMAGING,1996,14(7-8):945-946.
APA	Ye, CH,Deng, F,&Du, YR.(1996).Solid-state NMR investigation of acid sites in dealuminated HZSM-5 zeolite.MAGNETIC RESONANCE IMAGING,14(7-8),945-946.
MLA	Ye, CH,et al."Solid-state NMR investigation of acid sites in dealuminated HZSM-5 zeolite".MAGNETIC RESONANCE IMAGING 14.7-8(1996):945-946.