Ab initio simulation of Lewis sites in mordenite and comparative study of the strength of active sites via CO adsorption

Lubomir Benco, Tomas Bucko, Juergen Hafner, Hervé Toulhoat

    Veröffentlichungen: Beitrag in FachzeitschriftArtikelPeer Reviewed

    Abstract

    Ab initio density-functional investigations of intrazeolite active centers have been performed for mordenite. We investigate die structure and properties of bare Al3+ cations bound to the framework and originating from extra-framework Al(H2O)63+ cations dehydrated at severe thermal treatment of the zeolite. A bare Al3+ cation in the zeolite causes either a limited local relaxation or is trapped in a small ring of the zeolite structure without substantial relaxation of the framework. Such a cation behaves as a strong Lewis site. The strength of trapped Al 3+ is evaluated via the adsorption of CO and compared to a variety of zeolite active centers such as Brønsted sites, Na-counterions, and surface silanols. An overall agreement between experimental and calculated shifts of the CO stretching frequency is observed. The comparison of bare and hydrated Al3+ and Ga3+ cations shows that stretching frequencies blue-shifted to ?2230 cm-1 can originate only from adsorption on bare cations. In zeolites not containing any exchanged extra-framework cations the presence of stretching bands at ?2230 thus cm-1 evidences the presence of highly active bare Al3+ trapped in five-membered rings of the zeolite framework.
    OriginalspracheEnglisch
    Seiten (von - bis)13656-13666
    Seitenumfang11
    FachzeitschriftThe Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical
    Jahrgang108
    Ausgabenummer36
    DOIs
    PublikationsstatusVeröffentlicht - 2004

    ÖFOS 2012

    • 1030 Physik, Astronomie

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