日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

A series of catalysts containing tris(2,2'-bipyridine)iron(II) (Fe(bpy)₃²⁺) complexes inside zeolite Y cages with various extraframework alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) have been synthesized via a "ship-in-a-bottle" method. Formation of the Fe(bpy)₃²⁺ complexes was ascertained by XRD, diffuse-reflectance UV-vis spectroscopy, and Fe K-edge XAFS measurement. The steric constraint induced by increasing the size of the alkali metal cations resulted in a decrease in both Fe content and BET surface area. The intensity of the MLCT absorption band of Fe(bpy)₃²⁺ complexes associated with zeolites increased in the presence of heavier alkali metal cations, while the electron density of the Fe atoms decreased as the ionic radius of the alkali metal cations increased. The encapsulation of Fe(bpy)₃²⁺ within zeolite Y cages resulted in the creation of a new photocatalytic system enabling efficient oxidation of styrene to benzaldehyde and styrene oxide under visible-light irradiation (_λ > 430 nm) in the presence of molecular oxygen (O₂). The turnover number (TON) was found to correlate with the increased intensity of the MLCT band and the decreased electron density of the Fe atoms. Additionally, Ru(bpy)₃²⁺ complexes contained within a series of zeolite Y cages with various extra framework alkali metal cations were successfully synthesized. The intensity of the photoluminescence spectra of Ru(bpy)₃²⁺ complexes associated with zeolites increased in the presence of lighter alkali metal cations. This result was found to corroborate with the increased TON for the photo-induced oxidation of styrene derivatives under visible-light irradiation and in the presence of O₂. This suggests that the electronic configuration of the lowest triplet state of Ru(bpy)₃²⁺ can be enhanced with the aid of light alkali metal cations, which predominantly determine the intensity of photoluminescence and the photooxidation rate.