US EPA

7671713 

Journal Article 

Adsorption of n-hexane in zeolite-5A: a temperature-programmed desorption and IR-spectroscopic study 

Sivasankar, N; Vasudevan, S 

2005 

Yes 

Journal of Physical Chemistry B
ISSN: 1520-6106
EISSN: 1520-5207 

109 

32 

15417-15421 

English 

16852955 

10.1021/jp0518714 

WOS:000231178000034 

The adsorption and desorption of n-hexane over Zeolite-5A has been investigated as a function of loading using simultaneous Fourier transform infrared (FTIR)-temperature-programmed desorption (TPD) measurements. The TPD profiles show a second peak developing at lower temperatures when loading exceeds 16 hexane molecules per Zeolite-5A unit cell or two molecules per alpha-cavity of the Zeolite-5A structure. The infrared spectra rule out two types of adsorption sites as the origin of the two peaks in the TPD. Changes in the conformation of the adsorbed hexane as a function of loading and temperature were followed by monitoring the position of the methylene stretching modes in the infrared spectra. With increasing loading, the adsorbed hexane adopts a stretched trans conformation. These changes occur at loading levels below 12 hexane molecules per Zeolite-5A unit cell. No change is observed above this loading, ruling out any conformational change at loadings where the second peak is seen in the TPD. The second peak in the TPD arises, therefore, from a combination of steric repulsion and loss of translational entropy.