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

Zeolites are crystalline microporous materials that are attracting much attention owing to their applications as high-performance catalysts, in separation processes, and in optical, magnetic, and electronic devices. Major efforts have been undertaken to synthesize large single crystals with a well-defined habit, because some applications require large zeolite crystals to allow effective use of their micropores. In 1971 Charnell synthesized zeolite Na-A (LTA) crystals (ca. 65 µm) and zeolite Na-X (FAU) crystals (ca. 140 µm) under hydro-thermal conditions from gels of sodium metasilicate, sodium aluminate, and triethanolamine, which were purified to remove particles by a precision filtration technique. In 1993 a novel method to synthesize zeolites in nonaqueous media was developed to obtain giant zeolite crystals by controlling the release and solubility of reactive solution species in organothermal systems. Other attempts to obtain large zeolite crystals have also been made. Recently, we developed a novel technique for synthesizing giant zeolite crystals in aqueous media by controlling the solubility in hydrothermal systems. Both silicalite-1 (all-silica MFI) and analcime (ANA) crystals with sizes of about 3 mm, which were unknown until now, were successfully synthesized by using bulk materials as the silica and alumina sources (bulk-material dissolution (BMD) technique).