FORMATION AND GROWTH OF A RU CLUSTER IN A Y-ZEOLITE SUPERCAGE PROBED BY XE-129 NMR-SPECTROSCOPY AND XENON ADSORPTION MEASUREMENTS

Abstract

Rutbenium was supported as a ruthenium-red complex ion on NaY zeolite by stirring the zeolite powder in an aqueous solution of RuCl3 containing ammonia at 3.50 K. The formation of a Ru cluster in the zeolite supercage due to the reduction of the Ru complex and subsequent growth of the Ru cluster upon heating in vacuum, H-2, and 02 were studied by the measurement of xenon adsorption on Ru, the Xe-129 NMR spectrum of the adsorbed xenon, the transmission electron micrograph, and the extended X-my absorption fine structure of Ru. The results showed that very small Ru clusters consisting of ca. 20 Ru atoms on average can be obtained in the supercage due to the autoreduction of the supported ruthenium species during the evacuation of the sample under heating to 673 K, and the average number of Ru atoms per cluster gradually increased to 50 upon further beating to 823 K both in H-2 and under vacuum. The xenon adsorption data indicated that the exposure of the 20-atom cluster to O2 resulted in much more severe increase of the cluster size than that caused by H-2 and vacuum at the same temperature, e.g., increasing the average number of Ru atoms per cluster to 45 after the exposure to 1 atm of O2 at room temperature and resulting in the formation of large Ru agglomerates greater than 100 nm on the external surface of the zeolite crystal after exposure to O2 at 673 K.