Preparation of small nickel-oxide cluster by hydrolysis of NiY and activity for CO oxidation

Abstract

Ni2+-exchanged zeolite Y(NiY) was treated with an aqueous NaOH or ammonia solution in order to prepare the small clusters of nickel hydroxide in the zeolite matrix. The preferential hydrolysis for only the Ni2+ ions inside the supercages proceeded by soaking NiY with the NaOH solution in a range of pH 9.0–10.0. A significant hydrolysis of the Ni2+ ions was induced by the treatment above pH 10.5, accompanying the migration of the Ni2+ ions situated inside the sodalite cages and hexagonal prisms. Consequently, the complete hydrolysis of the Ni2+ ions introduced in zeolite Y was achieved at pH 10.8–11.0. On the contrary, only a part of the Ni2+ ions was hydrolysed by the NH4OH treatment even at pH 12.0. Small nickel-oxide clusters were formed inside the supercages by calcining the NaOH-treated NiY at 643 K in air, which exhibited the enhanced activity for CO oxidation.