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Crystallization Mechanism of a Family of Embedded Isoreticular Zeolites
- Min, Jung Gi, Choi, Hyun June, Shin, Jiho, Hong, Suk Bong
- The Journal of Physical Chemistry C 2017 v.121 no.30 pp. 16342-16350
- adsorption, carbon, carbon dioxide, crystallization, ions, nuclear magnetic resonance spectroscopy, prediction, stable isotopes, tetraethylammonium compounds, zeolites
- We have recently been successful in predicting and synthesizing a series of body-centered cubic zeolites with expanding structural complexity and embedded isoreticular structures, termed the RHO family. Here we propose a plausible formation pathway for ECR-18, ZSM-25, and PST-20, the three members of this zeolite family, in the presence of tetraethylammonium ions as an organic structure-directing agent, based on the ¹³C MAS NMR, IR, and CO₂ adsorption results obtained from the solid products recovered as a function of time during their crystallization processes, together with the quantum-chemical calculation results. The nucleation of these three zeolites, all of which consist of seven different structural units, begins with the almost simultaneous construction of 26-hedral lta and 14-hedral t-plg cages and their subsequent connection via shared 8-rings in the diagonal direction of the cubic unit cell. As a logical next step, 8-hedral t-oto and 12-hedral t-phi cages are built around the preorganized t-plg cages. The remaining embedded spaces are readily filled up with 10-hedral t-gsm cages, as well as with t-oto and t-phi cages. Finally, 10-hedral d8r and 14-hedral pau cages are alternately constructed along the cubic edges. Over the outer surface of the resulting nuclei of the RHO family zeolites, the crystal growth may occur in a similar manner as described above.