A Periodic DFT Study of N2O4 Disproportionation on Alkali-Exchanged Zeolites X

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• 作者：Evgeny A. Pidko ; Pierre Mignon ; Paul Geerlings ; Robert A. Schoonheydt ; Rutger A. van Santen
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：April 10, 2008
• 年：2008
• 卷：112
• 期：14
• 页码：5510 - 5519
• 全文大小：814K
• 年卷期：v.112,no.14(April 10, 2008)
• ISSN：1932-7455

文摘

Adsorption and disproportionation of dinitrogen tetraoxide on sodium-, potassium-, and rubidium-exchangedzeolites X with Si/Al ratio of 1.18 were studied using density functional theory calculations with periodicboundary conditions. It is found that the stabilization and activation of most of the N₂O₄ isomers confined inthe zeolitic cage does not follow Lewis acidity difference of the extraframework cations. This is also observedfor the energetics of the N₂O₄ disproportionation reaction resulting in formation of a space-separatedNO⁺···NO₃^- ion pair. The reaction energy increases in the row NaX < RbX < KX. The strength ofperturbations and, therefore, the low-frequency shift of the N-O stretching frequency of the adsorbed NO⁺cations correlate well with the basicity of the zeolite (RbX > KX > NaX). However, this factor is not therelevant reactivity parameter for the N₂O₄ disproportionation in the cationic forms of zeolites. The higheractivity for the disproportionation as well as the stronger molecular adsorption of N₂O₄ on RbX and KXzeolites as compared to that on NaX is ascribed to the features analogous to the molecular recognitioncharacteristics of supramolecular systems. The steric properties of the zeolite cage and the mobility of theextraframework cations induced by adsorption are essential to shape the optimum configuration of the activesite for N₂O₄ disproportionation.