FT-IRおよび水の吸着によるHZSM-5ゼオライトの脱アルミニウム挙動の検討 <論文>

Studies on the Dealumination Behavior of HZSM-5 Zeolite by FT-IR and Water Vapor Adsorption

Iwami Yoshihiro

Nakajima Yusuke

Sano Tsuneji

Kawakami Yusuke

日本化学会誌 : 化学と工業化学

Journal of the Chemical Society of Japan : chemistry and industrial chemistry

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。

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.

Chemistry [ 430 ]

jpn

日本化学会

Copyright (c) 1996 The Chemical Society of Japan

[ISSN] 0369-4577

[NCID] AN00186595

[DOI] 10.1246/nikkashi.1996.617

[DOI] https://doi.org/10.1246/nikkashi.1996.617