Accelerated Crystallization of LTA Zeolite Using a Combination of High-Silica FAU Zeolite with Low Crystallinity and Additional Al Sources

Synthesis methods and crystallization mechanisms of LTA zeolites have been studied by various approaches such as using alkali metal hydroxides, organic structure-directing agent cations, or fluoride anions, so that the understanding of the crystallization pathway is one of particular interest. As a fundamental research, we succeeded in synthesizing a highly crystalline LTA zeolite by combining dealuminated FAU with low crystallinity and an additional aluminum source (Al(OH)3). The crystallization rate of the LTA zeolite was higher than that from conventional colloidal silica (Ludox HS-40) and Al(OH)3. In addition, there was a large difference in the particle size distribution of the as-made LTA zeolites. Furthermore, when using dealuminated FAU and Al(OH)3, Al-rich aluminosilicate species with four-ring structures were observed in the initial induction period, after which the gradual incorporation of TMA+ cations into sod cages of the LTA zeolite was found. Based on the obtained results, a crystallization scheme for LTA zeolites synthesized using zeolitic sources of dealuminated FAU as starting materials is proposed, which deepens the understanding of the crystallization pathway of LTA zeolite.