Synthesis of a Specified,Silica Molecular Sieve by Using Computationally Predicted Organic Structure‐Directing Agents

Crystalline molecular sieves are used in numerous applications, where the properties exploited for each technology are the direct consequence of structural features. New materials are typically discovered by trial and error, and in many cases, organic structure‐directing agents (OSDAs) are used to direct their formation. Here, we report the first successful synthesis of a specified molecular sieve through the use of an OSDA that was predicted from a recently developed computational method that constructs chemically synthesizable OSDAs. Pentamethylimidazolium is computationally predicted to have the largest stabilization energy in the STW framework, and is experimentally shown to strongly direct the synthesis of pure‐silica STW. Other OSDAs with lower stabilization energies did not form STW. The general method demonstrated here to create STW may lead to new, simpler OSDAs for existing frameworks and provide a way to predict OSDAs for desired, theoretical frameworks.     

EU‐12: A Small‐Pore,High‐Silica Zeolite Containing Sinusoidal Eight‐Ring Channels

Zeolite EU‐12, the framework structure of which has remained unsolved during the past 30 years, is synthesized at a specific SiO₂/Al₂O₃ ratio using choline as an organic structure‐directing agent, with both Na⁺ and Rb⁺ ions present. Synchrotron powder X‐ray diffraction and Rietveld analyses reveal that the EU‐12 structure has a two‐dimensional 8‐ring channel system. Among the two distinct 8‐ring (4.6×2.8 and 5.0×2.7 Å) channels along c axis, the smaller one interconnects with the sinusoidal 8‐ring (4.8×3.3 Å) channel along a axis. The other large one is simply linked up with the sinusoidal channel by sharing 8‐rings (4.8×2.6 Å) in the ac plane. The proton form of EU‐12 was found to show a considerably higher ethene selectivity in the low‐temperature dehydration of ethanol than H‐mordenite, the best catalyst for this reaction.     

Targeted Synthesis of a Zeolite with Pre‐established Framework Topology

Given their great potential as new industrial catalysts and adsorbents, the search for new zeolite structures is of major importance in nanoporous materials chemistry. However, although innumerable theoretical frameworks have been proposed, none of them have been synthesized by a priori design yet. We generated a library of diazolium‐based cations inspired from the organic structure‐directing agents (OSDAs) recently reported to give two structurally related zeolites (PST‐21 and PST‐22) under highly concentrated, excess‐fluoride conditions and compared the stabilization energies of each OSDA cation in ten pre‐established hypothetical structures. A combination of the ability of the OSDA selected in this way with the excess‐fluoride approach has allowed us to crystallize PST‐30, the targeted aluminosilicate zeolite structure. We anticipate that our approach, which aims to rationally couple computational predictions of OSDAs with an experimental setup, will advance further development in the synthesis of zeolites with desired properties.