Enhancement in reducibility of cobalt ions in CoNaY by treatment with alkali-metal hydroxides

Abstract

Cobalt-containing Y-zeolites, prepared by ion exchange and treatment with aqueous alkali-metal hydroxide solution, have been investigated. The reducibility of cobalt ions in each site of zeolite Y was investigated by TPR. X-Ray diffraction, FTIR spectroscopy, UV–VIS DRS and Xe adsorption were used to investigate the effect of sodium hydroxide treatment. The cobalt ions in the sites, S_I and S_I migrated to the sodalite cage and supercage after treatment with aqueous sodium hydroxide. The extent of migration was related to the concentration of sodium hydroxide and the cobalt loading. The amounts of cobalt ions located at various sites were estimated from the area of each TPR peak. The other alkali-metal hydroxides, KOH and LiOH, showed a similar effect. Cobalt species in the supercage and on the exterior surface of the zeolite after treatment with sodium hydroxide solution were shown to be CoO(OH) by the IR band at 3631 cm^–1 which was oxidized to Co₃O₄ during calcination at 623 K. The formation of cobalt metal clusters is facilitated by treatment with sodium hydroxide solution and by subsequent reduction with hydrogen.