Influence of Brnsted acidity on the redox properties of silver species in zeolite mordenite

Abstract

The redox behaviour of Ag⁺ ions exchanged into zeolites is strongly influenced by the presence and concentration of Brønsted acid sites (BS). This is demonstrated by a temperature programmed reduction study of various samples prepared by ion exchange into the Na⁺ form or by impregnation of the H⁺ form of mordenite with AgNO₃ solution. The Brønsted acidity of the latter was varied by different ways of transforming the NH₄⁺ form to the H⁺ form. High concentration of BS as well as a high Ag loading favours the reoxidation of A formed in the reduction process. On acidic, Ag-loaded mordenites, a complete reduction of Ag⁺ occurs only at relatively high temperatures (above 600°C) where the BS are progressively destroyed.