Characterization of alkali exchanged ZSM5 by IR spectrosopy

Temperature-programmed desorption (TPD) and in situ Fouriertransform infrared (FT-IR) spectroscopic methods were employed to investigate the effect of loading and sample temperature on the state of benzene molecules inside the channels of NaZSM-5 zeolite. TPD profiles revealed the existence of at least three distinct states of benzene adsorption, characterized by desorption peak maxima at ca. 120 ο C, 170 ο C and 220 ο C, respectively. Based on the growth behaviour of these bands, it is suggested that the benzene molecules occupy sinusoidal channels, straight channels and external surfaces, in that order. A reverse trend was observed during the subsequent flushing of the sample at varying temperatures. A virtually fixed amount of benzene was occluded at these three locations, depending upon the loading. The FT-IR studies revealed that the benzene molecule exists in a compressed state in the zeolitic channels, with the molecular clusters formed in the process dispersing only at temperatures above 150 ο C. For initial benzene loadings of up to ca. 1.5 molecules/unit cell, the spectrum obtained showed that in the O-H stretch region the bridge-bonded OH groups and hydroxyl groups associated with the internal zeolitic channels were perturbed simultaneously. The results show that even for a loading lower than necessary for saturation, a considerable amount of benzene remains condensed at the external surface of ZSM-5 zeolite.

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The Temperature-Dependent Adsorption Behaviour of Benzene Molecules in ZSM-5 Zeolite Pores: TPD and FT-IR Spectroscopy Studies

Sahasrabudhe

Varma

Gupta

2005

Adsorption Science & Technology

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Characterization of alkali exchanged ZSM5 by IR spectrosopy

Abstract: The use of time resolved FTIR spectroscopy for characterizing time dependent adsorbate concentrations has been demonstrated with the examples of adsorption/desorption of ammonia and of adsorption and reactions of propan-2-ol. Adsorption sites and adsorbate structures are discussed.

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The Temperature-Dependent Adsorption Behaviour of Benzene Molecules in ZSM-5 Zeolite Pores: TPD and FT-IR Spectroscopy Studies

The Temperature-Dependent Adsorption Behaviour of Benzene Molecules in ZSM-5 Zeolite Pores: TPD and FT-IR Spectroscopy Studies

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