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ID 46485
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title alternative
Studies on the Dealumination Behavior of HZSM-5 Zeolite by FT-IR and Water Vapor Adsorption
creator
Iwami, Yoshihiro
Nakajima, Yusuke
Kawakami, Yusuke
NDC
Chemistry
abstract
スチーミングおよび熱処理により脱アルミニウム率の異なる種々の HZSM-5 ゼオライトを調製し,その FT-IR スペクトルおよび水の吸着から水蒸気雰囲気下での HZSM-5 ゼオライトの脱アルミニウム挙動を検討した。その結果,脱アルミニウムの速度は水蒸気分圧に大きく依存すること,およびゼオライト骨格構造中のアルミニウムの 4 本の A1-O 結合は一度に加水分解されるのではなく,逐次的に加水分解されることが明らかとなった。すなわち,脱アルミニウムは少なくとも(1) 4本の Al-O 結合のうち一部の結合が切断される過程および(2)このアルミニウム種の残りの結合がさらに切断されてゼオライト骨格構造から完全に脱離する過程からなっている。
また,脱アルミニウム処理後のゼオライトによる水の吸着実験から,ゼオライト骨格構造中のアルミニウムの 4 本の結合のうち一部の結合が切断されたアルミニウム種は水の吸着を阻害しないが,骨格構造から完全に脱離したアルミニウム種は水の吸着を著しく阻害することが明らかとなった。
abstract
To clarify the dealumination behavior of zeolite during steaming, HZSM-5 zeolites with various degrees of dealumination were prepared by steaming and thermal treatment. The dealuminated zeolites were characterized by using FT-IR and water vapor adsorption. It was found that the dealumination rate is strongly dependent on the water vapor pressure. It was also found that the dealumination of HZSM-5 zeolite by steaming consists of two steps at least; the first step is a partial hydrolysis of four A1-O bonds of the framework aluminum, and the second step is a complete release of the alumin um from the zeolite framework.
Adsorption of n itrogen and water vapor was also studied to evaluate the state of nonframework aluminum in the zeolitic pore. The micropore volumes W0(N2) of the dealuminated zeolites calculated by the D-R plot of the adsorption isotherms of nitrogen hardly depended upon the degree of dealumination, indicating that the dealuminated zeolites maintain their framework structure. However, the micropore volumes W0(N2) from the adsorption isotherms of water vapor depended on the dealumination condition. In the case of the zeolites dealuminated by mild steaming or thermal treatment, the micropore volumes W0(N2) were consistent with those of untreated zeolites with the same concentration of framework aluminums. In the case of zeolites dealuminated by severe steaming, however, the micropore volumes W0(N2) were smaller than those expected from the concentration of framework aluminums. This suggests that the nonframework aluminum species released completely from the zeolite framework suppress strongly the adsorption of water molecules into the zeolitic pores.
description
本研究は文部省科学研究費助成金重点領域研究「特殊反応場の触媒化学―極限環境触媒―」の助成によって行われた.
journal title
Journal of the Chemical Society of Japan : chemistry and industrial chemistry
volume
Volume 1996
issue
Issue 7
start page
617
end page
623
date of issued
1996-07-10
publisher
日本化学会
issn
0369-4577
ncid
publisher doi
language
jpn
nii type
Journal Article
HU type
Journal Articles
DCMI type
text
format
application/pdf
text version
publisher
rights
Copyright (c) 1996 The Chemical Society of Japan
relation url
department
Graduate School of Engineering