High resolution adsorption isotherms of N2 and Ar for nonporous silicas and MFI zeolites |
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Authors: | Kazuyuki Nakai Joji Sonoda Masayuki Yoshida Masako Hakuman Hiromitsu Naono |
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Institution: | (1) BEL-Japan, INC, Haradanaka, Toyonaka-shi, Osaka 561-0807, Japan |
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Abstract: | The high resolution adsorption isotherms of N2 (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm2) and for two MFI zeolite with different Al contents (Si/Al=12.5 and 500). Silanol groups and Al sites (acid sites) gives
the significant effect on the N2 isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are
preferable in calculation of microporosity of zeolites. The N2 and Ar isotherms for MFI zeolite (Si/Al=500) have been measured at temperatures of 77–94 K, from which the differential adsorption
energies of N2 and Ar are calculated. The interaction of N2 with channel surface of MFI zeolite is greater than that of Ar in the range of α
s
=0.1–0.7. The hystereses are detected for the N2 isotherm in p/p
o=0.1–0.3 at 77.4 K and for the Ar isotherm in p/p
o=3×10−4–2×10−3 at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy. |
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Keywords: | MFI zeolite ZSM-5 Silicalite Adsorption isotherms of N2 and Ar Differential adsorption energy |
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