Construction of Paired Al Sites in High-Silica Mfi-Type Zeolite Framework Via Transcription-Induced Method

Paired Al sites were formed in high-silica MFI-type zeolite frameworks with Si/Al molar ratios of 11–13 via the transcription-induced method, where Al-rich amorphous silica-alumina enriched with paired Al species was employed as a zeolite precursor. Quantification by the Co2+ titration technique demonstrated that the aging time for the precursor in synthesis gels prior to the hydrothermal treatment was the key to controlling the amount of paired Al sites in the MFI-type frameworks. Ultraviolet-visible spectra of the Co2+-exchanged MFI-type zeolites indicated that the paired Al sites captured bare Co2+ without any oxygen-containing ligands, and also that most of the paired Al sites were present at the channel intersections of the MFI-type framework.