Stability of silver clusters in mordenites with different SiO2/Al2O3 molarratio

The stability and decay of silver clusters characterized by absorption band s 320 and 285 nm incorporated in mordenites with different SiO2/Al2O3 molar ratios were studied under ambient conditions. Significantly different rate s of disappearance of these two bands were the basis for assigning them to different silver species. Oxidation converts the clusters peaking at 320 an d 285 nm into other silver clusters characterized by absorption bands at 31 0 and 240 nm, respectively. The oxidation of silver clusters peaking at 285 nm is significantly faster than that at 320 nm. The stability of both orig inal clusters decreases with acid site strength that, in its turn, depends on SiO2/Al2O3, molar ratio. The minimum lifetime of clusters peaking at 320 and 285 nm equal to ca. 40 and 20 days, respectively, was observed for mor denite characterized by the strongest acid sites. For mordenites possessing weaker acid sites, the lifetime of these clusters is found to be more than 50 months. The oxidation of silver clusters is reversible, and re-reduced silver clusters were revealed to possess the same electron structure as ori ginal ones. (C) 1999 Published by Elsevier Science B.V. All rights reserved .