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题名: Crystallization and Si incorporation mechanisms of SAPO-34
作者: Tan, J;  Liu, ZM;  Bao, XH;  Liu, XC;  Han, XW;  He, CQ;  Zhai, RS
关键词: mechanism ;  molecular sieves ;  SAPO-34 ;  synthesis ;  characterization
刊名: MICROPOROUS AND MESOPOROUS MATERIALS
发表日期: 2002-06-01
卷: 53, 期:1-3, 页:97-108
收录类别: SCI
文章类型: Article
WOS标题词: Science & Technology ;  Physical Sciences ;  Technology
类目[WOS]: Chemistry, Applied ;  Chemistry, Physical ;  Nanoscience & Nanotechnology ;  Materials Science, Multidisciplinary
研究领域[WOS]: Chemistry ;  Science & Technology - Other Topics ;  Materials Science
英文摘要: In this study of the synthesis of SAPO-34 molecular sieves, XRD, SEM, XRF, IR and NMR techniques were applied to monitor the crystalloid, structure and composition changes of the samples in the whole crystallization process in order to get evidence for the crystallization as well as Si incorporation mechanism of SATO-34. XRD results revealed that the crystallization contained two stages. In the first 2.5 h (the earlier stage), high up to similar to80% of relative crystallinity could be achieved and the crystal size of SAPO-34 was almost the same as that of any longer time, indicating a fast crystallization feature of the synthesis. In this stage, IR revealed that the formation of SAPO-34 framework structure was accompanied by the diminution of hydroxyls, suggesting that crystal nuclei of SAPO-34 may arise from the structure rearrangement of the initial gel and the condensation of the hydroxyls. NMR results reveal that the template and the ageing period are crucial for the later crystallization of SAPO-34. Preliminary structure units similar to the framework of SAPO-34 have already formed before the crystallization began (0 h and low temperature). Evidence from IR, NMR, and XRF shows that the formation of the SAPO-34 may be a type of gel conversion mechanism, the solution support and the appropriate solution circumstance are two important parameters of the crystallization of SAPO-34. Meanwhile, NMR measurements demonstrated that about 80% of total Si atoms directly take part in the formation of the crystal nuclei as well as in the growth of the crystal grains in the earlier stage (<2.5 h). Evidence tends to support that Si incorporation is by direct participation mechanism rather than by the Si substitution mechanism for P in this stage (<2.5 h). In the later stage (>2.5 h), the relative content of Si increased slightly with a little decrease of Al and P. The increase of Si(4Al) and the appearance of the Si(3Al), Si(2Al), Si(1Al) and Si(OAl) in this stage suggest that substitution of the Si atoms for the phosphorus and for the phosphorus and aluminum pair takes place in the crystallization. The relationship among structure, acidity and crystallization process is established, which suggests a possibility to improve the acidity and catalytic properties by choosing a optimum crystallization time, thus controlling the number and distribution of Si in the framework of SAPO-34. (C) 2002 Elsevier Science Inc. All rights reserved.
关键词[WOS]: SOLID-STATE NMR ;  MOLECULAR-SIEVES ;  SILICON INCORPORATION ;  CATALYTIC CONVERSION ;  METHANOL ;  ZEOLITES
语种: 英语
原文出处: 查看原文
WOS记录号: WOS:000176020100010
Citation statistics: 
内容类型: 期刊论文
URI标识: http://cas-ir.dicp.ac.cn/handle/321008/83761
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

Recommended Citation:
Tan, J,Liu, ZM,Bao, XH,et al. Crystallization and Si incorporation mechanisms of SAPO-34[J]. MICROPOROUS AND MESOPOROUS MATERIALS,2002,53(1-3):97-108.
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