# Adsorption of n-Hexane in Zeolite-5A: A Temperature-Programmed Desorption and IR-Spectroscopic Study

Sivasankar, N and Vasudevan, S (2005) Adsorption of n-Hexane in Zeolite-5A: A Temperature-Programmed Desorption and IR-Spectroscopic Study. In: Journal of physical chemisty B, 109 (32). pp. 15417-15421.

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## Abstract

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 here 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.

Item Type: Journal Article Copyright of this article belongs to American Chemcial Society. Division of Chemical Sciences > Inorganic & Physical Chemistry 04 May 2007 19 Sep 2010 04:37 http://eprints.iisc.ernet.in/id/eprint/10818