H+/Na+ ion equilibria of ZSM-5 with respect to surface composition

Titelangaben

Dubbe, Andreas ; Moos, Ralf:
H+/Na+ ion equilibria of ZSM-5 with respect to surface composition.
2007
Veranstaltung: 19. Deutsche Zeolith-Tagung , 07.-09.03.2007 , Leipzig, Deutschland.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Sonstige Präsentationstyp)

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Abstract

The zeolite ZSM-5 (MFI) is used as solid-state ion conducting material for electrochemical applications including gas sensors. Zeolites with defined ion composition in the micropores are commonly prepared by ion exchange in aqueous solutions. However, for properties such as electrode kinetics and grain boundary conductivity, the composition at the surfaces of the single zeolite crystals is of crucial importance and should be controlled. In order to achieve this, we have to study the ion exchange equilibria of the surface sites. Aim of the present study is to gain information about the ion equilibria of the surface sites by pH measurements of Na-ZSM-5 suspensions in dependence of Na+ and H3O+ addition in aqueous solutions. The ionic equilibria of both surface and volume sites are modelled under consideration of concentration dependent ion activities, which are well known for aqueous HCl-NaCl solutions. The results allow us to determine preparation conditions for zeolites with controlled surface ion compositions.