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

The redox behaviour of Ag+ ions exchanged into zeolites is strongly influenced by the presence and concentration of Bronsted 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 Bronsted 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 Ag-0 formed in the reduction process. On acidic, Ag-loaded mordenites, a complete reduction of Ag+ occurs only at relatively high temperatures (above 600 degrees C) where the BS are progressively destroyed.