PREPARATION OF IRIDIUM CLUSTERS IN ZEOLITE-Y VIA CATION-EXCHANGE - EXAFS, XENON ADSORPTION, AND XE-129 NMR-STUDIES

Abstract

The conversion of [Ir(NH3)(5)Cl](2+) and [Ir(NH3)(5)(H2O)](3+) to 1-nm Ir clusters entrapped in the supercages of NaY zeolite has been investigated by using Xe-129 NMR spectroscopy, xenon adsorption, and extended X-ray absorption fine structure. The cation exchange with [Ir(NH3)(5)Cl](2+) was achieved by slurring NaY in an aqueous solution of [Ir(NH3)(5)Cl]Cl-2 at room temperature. The cation exchange with [Ir(NH3)(5)(H2O)](3+) employed either an aqueous solution of [Ir(NH3)(5)(H2O)](ClO4)(3) at room temperature or an aqueous solution of IrCl3 containing NH3 at a temperature of 330 K. This paper reports very distinctive pretreatment requirements for the transformation of these two ionic precursors to 1-nm Ir clusters in the zeolite supercages: activation in O-2 flow at 573 K is required in the,case of [Ir(NH3)(5)Cl](2+), while outgassing at 473 K is sufficient in the case of [Ir(NH3)(5)(H2O)](3+), prior to the final reduction with H-2. This second method, which has not been previously described, provides a convenient route for the preparation of Ir clusters in zeolites without using an oxidative treatment, and avoiding Cl-containing species. Furthermore, results from Xe-129 NMR and xenon adsorption measurements indicate that the cluster size is substantially smaller than that in the case of [IT(NH3)(5)Cl](2+). (C) 1994 Academic Press, Inc.