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题名: Investigation of the Physicochemical Changes Preceding Zeolite Nucleation in a Sodium-Rich Aluminosilicate Gel
作者: Itani, Lama2;  Liu, Yong1;  Zhang, Weiping1;  Bozhilov, Krassimir N.4;  Delmotte, Luc2;  Valtchev, Valentin3
通讯作者: 张维萍 ;  Valentin Valtchev
刊名: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
发表日期: 2009-07-29
DOI: 10.1021/ja902088f
卷: 131, 期:29, 页:10127-10139
收录类别: SCI
文章类型: Article
部门归属: 5
项目归属: 502
产权排名: 2;2
WOS标题词: Science & Technology ;  Physical Sciences
类目[WOS]: Chemistry, Multidisciplinary
研究领域[WOS]: Chemistry
英文摘要: All industrially available zeolites are obtained from hydrogel systems. Unfortunately the level of understanding of the events preceding zeolite crystallization is far from satisfactory. In this respect, revealing the nature of the processes taking place in the precursor gel is of paramount importance to understanding zeolite nucleation. The investigation of the gel structure, however, is a difficult task due to the complexity of the object in terms of both composition and topology. Therefore, a combination of hyperpolarized (HP) (129)Xe NMR-N(2) adsorption - high-resolution transmission electron microscopy-energy-dispersive spectrometry methods complemented by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and chemical analyses has been employed to study the changes in composition and structure of sodium hydroxide rich aluminosilicate gel yielding zeolite A. The role of each component in the system and the entire sequence of events during the induction, nucleation, and crystallization stages have been revealed. The high concentration of sodium hydroxide in the studied system has been found to control the size and structure of the gel particles in the beginning stage. During the initial polymerization of aluminosilicate species a significant part of the sodium hydroxide is expelled from the gel into the solution, which restricts extensive polymerization and leads to formation of small aluminosilicate particles with open pore structure. The induction period that follows is marked by incorporation of Na back in the bulk gel. The combined action of the Na ion as a structure-directing agent and the hydroxyl group as a mobilizer results in partial depolymerization of the gel and formation of voids with mesopore sizes. The nucleation maximum coincides temporally with development of pores with sizes in the range of 2-5 nm. The amorphous gel undergoes into crystalline zeolite only after these pores have disappeared and the chemistry of the gel has evolved to reach the stoichiometric zeolite composition. It was established unambiguously by high-resolution transmission electron microscopy and HP (129)Xe NMR that the nucleation of zeolite occurs in the solid part of the system and the succeeding crystallization commences only after the nuclei are released into the liquid, which is consistent with the autocatalytic mechanism. Also this investigation has demonstrated the unrivaled sensitivity of HP (129)Xe NMR that is capable of identifying presence of small amounts of crystalline zeolite material in amorphous medium with detection limit extending below 1 wt %.
关键词[WOS]: HYPERPOLARIZED XE-129 NMR ;  NA-A ZEOLITE ;  ROOM-TEMPERATURE ;  ELECTRON-MICROSCOPY ;  MAGNETIC-RESONANCE ;  MOLECULAR-SIEVES ;  CRYSTALLIZATION ;  GROWTH ;  MECHANISM ;  XENON
语种: 英语
原文出处: 查看原文
WOS记录号: WOS:000268395000060
Citation statistics: 
内容类型: 期刊论文
URI标识: http://cas-ir.dicp.ac.cn/handle/321008/102301
Appears in Collections:中国科学院大连化学物理研究所_期刊论文

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作者单位: 1.Chinese Acad Sci, Dalian Inst Chem Phys, State Key Lab Catalysis, Dalian 116023, Peoples R China
2.Univ Rennes 2, CNRS, Inst Sci Mat Mulhouse, LRC 7228, F-68093 Mulhouse, France
3.Univ Caen, Catalyse & Spectrochim Lab, ENSICAEN, CNRS, F-14050 Caen, France
4.Univ Calif Riverside, Cent Facil Adv Microscopy & Microanal, Riverside, CA 92521 USA

Recommended Citation:
Itani, Lama,Liu, Yong,Zhang, Weiping,et al. Investigation of the Physicochemical Changes Preceding Zeolite Nucleation in a Sodium-Rich Aluminosilicate Gel[J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY,2009,131(29):10127-10139.
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