Spectroscopic identification of adsorption properties of Zn2+ ions at cationic positions of high-silica zeolites with distant placing of aluminium ions.

G.M. Zhidomirov, A.A. Shubin, V.B. Kazansky, R.A. Santen, van

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Abstract

For Zn2+ cations in ZnZSM-5 zeolite unusual type of cationic positions, formed by two distantly placed framework aluminium atoms, is considered. Some extent of structural destabilization of cations in these cationic positions in comparison with traditional localization should result in promoted Lewis activity and adsorption activity of these sites. The last ones are manifested in the significantly increased IR low frequency shifts for adsorbed molecules and in their ability for heterolytic dissociation at elevating temperature. DFT cluster quantum chemical modeling of light alkane adsorption on Zn2+ in ZnZSM-5 zeolites confirms these conjectures in full agreement with recent experiments. Similar to the previously considered dihydrogen and methane molecule adsorption, we present here the calculations of ethane molecular and dissociative adsorption on these sites. It is shown that the unusually large ethane IR frequency shift recently observed in ZnZSM-5 zeolite can result from adsorptive interaction of C2H6 with Zn2+ stabilized in a cationic position with distantly placed aluminium ions. The dissociative adsorption of ethane molecules with the formation of bridged hydroxyl group and Zn–C2H5 structure is considered and an activation energy of ethylene formation from the alkyl fragment is evaluated.
Original languageEnglish
Pages (from-to)90-96
JournalTheoretical Chemistry Accounts
Volume114
Issue number1-3
DOIs
Publication statusPublished - 2006

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