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Experimental Determination of the Molar Absorption Coefficient of n ‐Hexane Adsorbed on High‐Silica Zeolites
Author(s) -
Gatti Giorgio,
Olivas Olivera Diana F.,
Sacchetto Vittoria,
Cossi Maurizio,
Braschi Ilaria,
Marchese Leonardo,
Bisio Chiara
Publication year - 2017
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201700481
Subject(s) - adsorption , zeolite , hexane , chemistry , microporous material , analytical chemistry (journal) , absorption (acoustics) , molecule , molecular sieve , materials science , organic chemistry , catalysis , composite material
Determination of the molar absorption coefficients of the CH 3 bending mode at ν ˜ =1380 cm −1 ( ϵ 1380 ) of n ‐hexane adsorbed from the gas phase on two different dealuminated zeolites is derived by a combination of IR spectroscopy and microgravimetric analysis. High‐silica zeolite Y (HSZ‐Y) and zeolite ZSM‐5 (with SiO 2 /Al 2 O 3 ratios of 200 and 280, respectively) with different textural and surface features are selected to evaluate the effect of the pore structure and architecture on the value of ϵ 1380 of the adsorbed n ‐hexane. Experimental data indicate that the molecule experiences a different adsorption environment inside zeolites; thus resulting in a significant change of the dipole moment and very different ϵ 1380 values: (0.278±0.018) cm μmol −1 for HSZ‐Y and (0.491±0.032) cm μmol −1 for ZSM‐5. Experimental data are also supported by computational modeling, which confirms the effect of different matrices on the IR absorption intensity. This study reveals that the use of probe molecules for quantitative measurements of surface sites has to be judiciously adopted, especially if adsorption occurs in the restricted spaces of microporous materials.