Zeolites are commercially used crystalline microporous materials. Understanding their crystallization mechanism and corresponding synthesis development is still of scientific and technological significance. Herein, we investigated the formation process of AEI zeolite using a combination of analysis methods, including X-ray diffractometry, nuclear magnetic resonance, and electrospray-ionization mass spectrometry, and developed a rational synthesis method without the use of a specific silica/alumina source (FAU zeolite). First, the synthesis condition was optimized by selecting a variety of synthesis components: FAU zeolites with different Al contents, colloidal silica, sodium aluminate, and three types of organic structure-directing agents (OSDAs). AEI zeolite preintroduced into the synthesis system (seed crystal) enabled its crystal growth from an easily available amorphous silica/alumina source. Stepwise gel preparation (SGP) through divided compositional control using an amorphous starting material effectively provided AEI zeolite in the presence of two types of OSDAs. A selected synthesis component (SGP with N,N-dimethyl-3,5-dimethylpiperidinium) formed AEI zeolite without even using AEI seed. Although the product contained a trace amount of impurity, it could be used as seed crystal for providing pure-phased AEI zeolite. Finally, from the merged synthetic and analytical results, we proposed that oligomeric aluminosilicate with a low dehydration degree contributes to AEI zeolite nucleation from an amorphous starting material. Furthermore, AEI zeolite catalyst with high activity and durability for emission-gas purification can be prepared by the SGP synthesis strategy. This comprehensive study would help rationally build zeolite synthesis and function design, particularly in a case that strongly depends on the starting material.

Aluminosilicate molecular-sieve zeolites are widely used in industrial processes, mostly as catalysts or adsorbents, and advances in the synthesis are still required in order to progress further applications. To further expand the zeolite synthesis system, herein we report the stepwise preparations of synthesis gels through divided compositional control; this strategy is applied to the effective synthesis of a CHA zeolite in the presence of an inexpensive organic structure directing agent (OSDA), benzyltrimethylammonium. Highly crystalline nanosized CHA zeolites were prepared at higher crystallization rates compared to those prepared using the conventional one-step gel-preparation method. The stepwise method also provided CHA zeolite in a wide range of starting gel compositions, and aluminum content within the formed CHA could be tuned. The aluminosilicate-formation process, investigated by the combination of analytical methods including X-ray diffractometry, NMR and Raman spectroscopy, and electrospray-ionization mass spectrometry (ESI-MS) and several synthetic experiments, revealed that the aluminosilicate cluster that forms in the highly alkaline aluminum-rich intermediate gel during the stepwise method helps to effectively form the CHA zeolite in the final synthesis step. We also demonstrate that this strategy is applicable to other synthesis systems with different OSDAs and target zeolites. Furthermore, the stepwise method provides efficient zeolite catalysts with high activities and durabilities for emission-gas purification applications. This sharable concept is expected to become a common tool that brings additional synthetic diversity to a variety of zeolite-synthesis systems.