Ž . Applied Surface Science 150 1999 58–64 www.elsevier.nlrlocaterapsusc Stability of silver clusters in mordenites with different SiO rAl O molar ratio 2 2 3 Nina E. Bogdanchikova a, ) , Vitalii P. Petranovskii a,b , Roberto Machorro M. a , Yoshihiro Sugi c , Victor M. Soto G. a,b , Sergio Fuentes M. a a Centro de Ciencias de la Materia Condensada, UNAM, Km. 107 Carret. Tijuana-Ensenada, Apdo Postal 2681, BC 22800, Mexico b CICESE, Km. 107 Carret. Tijuana-Ensenada, Apdo Postal 2732, BC 22800, Mexico c Gifu UniÕersity, Gifu 505-11, Japan Received 7 December 1998; accepted 21 March 1999 Abstract The stability and decay of silver clusters characterized by absorption bands 320 and 285 nm incorporated in mordenites with different SiO rAl O molar ratios were studied under ambient conditions. Significantly different rates of disappear- 2 2 3 ance of these two bands were the basis for assigning them to different silver species. Oxidation converts the clusters peaking at 320 and 285 nm into other silver clusters characterized by absorption bands at 310 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 original clusters decreases with acid site strength that, in its turn, depends on Si0 rAl O molar ratio. The minimum lifetime of 2 2 3 clusters peaking at 320 and 285 nm equal to ca. 40 and 20 days, respectively, was observed for mordenite 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 original ones. q 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 36.40.q;83.80.P Keywords: Silver clusters; Stability; Mordenites 1. Introduction Clusters in zeolites are perspective compounds for development of advanced materials for molecular electronics, quantum dotsrchains, zeolite electrodes, batteries and membranes, nonlinear optic materials, wx chemical sensors, etc. 1 . Silver catalysts including ) Corresponding author. UNAM, PO Box 439036, San Ysidro, CA 92143, USA. Tel.: q52-61-74-4602; Fax: q52-61-74-4603; E-mail: nina@ifisicaen.unam.mx Ag–mordenite are found to be active in NO removal from automotive sources causing serious environ- w x mental problems 2,3 . Silver is widely used in medicine due to its ability to catalyze the oxidative wx destruction of microorganisms 4 . It was revealed that clusters absorbing at 295 and 325 nm and interpreted as 8-atom silver clusters have a lifetime about 5 min in the presence of excess q wx Ag ions in aqueous solutions 5 . These clusters were called long-lived ‘magic’ clusters by Ershov et wx al. 5 . In the presence of a polyanion these clusters 0169-4332r99r$ - see front matter q 1999 Published by Elsevier Science B.V. All rights reserved. Ž . PII: S0169-4332 99 00223-8