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Issue 16, 2005
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On two alternative mechanisms of ethane activation over ZSM-5 zeolite modified by Zn2+ and Ga1+cations

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Abstract

The activation of ethane over zinc- and gallium-modified HZSM-5 dehydrogenation catalysts was studied by diffuse reflectance infrared spectroscopy. Hydrocarbon activation on HZSM-5 modified by bivalent Zn and univalent Ga cations proceeds via two distinctly different mechanisms. The stronger molecular adsorption of ethane by the acid–base pairs formed by distantly separated cationic Zn2+ and basic oxygen sites results already at room temperature in strong polarizability of adsorbed ethane and subsequent heterolytic dissociative adsorption at moderate temperatures. In contrast, molecular adsorption of ethane on Ga+ cations is weak. At high temperatures dissociative hydrocarbon adsorption takes place, resulting in the formation of ethyl and hydride fragments coordinating to the cationic gallium species. Whereas in the zinc case a Brønsted acid proton is formed upon ethane dissociation, decomposition of the ethyl fragment on gallium results in gallium dihydride species and does not lead to Brønsted acid protons. This difference in alkane activation has direct consequences for hydrocarbon conversions involving dehydrogenation.

Graphical abstract: On two alternative mechanisms of ethane activation over ZSM-5 zeolite modified by Zn2+ and Ga1+ cations

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Article information


Submitted
12 May 2005
Accepted
29 Jun 2005
First published
14 Jul 2005

Phys. Chem. Chem. Phys., 2005,7, 3088-3092
Article type
Paper

On two alternative mechanisms of ethane activation over ZSM-5 zeolite modified by Zn2+ and Ga1+ cations

V. B. Kazansky, I. R. Subbotina, N. Rane, R. A. van Santen and E. J. M. Hensen, Phys. Chem. Chem. Phys., 2005, 7, 3088
DOI: 10.1039/B506782K

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