EXAFS and optical spectroscopy characterisation of silver within zeolite matrices

Fiddy, S.G., Bogdanchikova, N., Petranovskii, V., Ogden, J.S. and Avalos-Borja, M. (2002) EXAFS and optical spectroscopy characterisation of silver within zeolite matrices. Journal of Surface Science and Catalysis, 142, 1939-1946.

Abstract

The study of silver-zeolite samples by a combination of EXAFS and Diffuse Reflectance UV-Visible spectroscopy has been utilised to discover the effect of the structural type and Si/Al ratio of zeolite matrix as well as influence of reduction temperature on the size, structure and oxidation of silver species stabilised inside zeolite voids. The preparation of silver-zeolite samples at high temperature using mordenite with medium Bronsted acid strength or at low temperature using mordenite with high acid strength leads to fast oxidation of reduced silver species. After reduction at medium temperatures silver clusters interpreted as Ag-8(0) and Ag-8(delta+) are formed in mordenites with intermediate Bronsted acid strength. The reduction of silver samples at high temperature utilising mordenite with a very small concentration of weak Bronsted acid sites leads to the formation of amorphous Ag particles. Deformation of the eight-atom clusters is more prominent in the erionite cavities, where space is more severely restricted than in mordenite channels. It is proposed that the charged Ag-8(delta+) clusters are more deformed than neutral Ag-8(0) clusters.

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