High-Silica, Enantiomerically Enriched STW-Type Molecular Sieves

Enantiomerically enriched molecular sieves can provide new opportunities for enantioselective catalysis and adsorption. The potential of using these materials for practical applications relies on the preparation of stable materials that can survive the rigors of use and regeneration. Reported enantiomerically enriched STW-type molecular sieves contain large amounts of Ge that limit the structural stability. Higher Si-containing STW-type molecular sieves will have enhanced stability, which should enable practical application. To achieve high-silica framework composition within enantiomerically enriched STW-type molecular sieves, a chiral organic structure-directing agent (OSDA) is computationally designed based on predicted stabilization energy toward the STW framework that is superior to previously employed OSDAs. With enantiopure forms of the designed OSDA, the synthesis of enantiomerically enriched STW-type germanosilicate molecular sieves with the framework Si/Ge as high as 18 is achieved. This high-silica STW-type molecular sieve has a significantly higher Si framework composition from the previously reported enantiomerically enriched germanium-rich STW-type molecular sieve and exhibits stability upon thermal treatment to 800 degrees C. The absolute stereochemistry of the framework structure is characterized by the dynamical refinement of microcrystal electron diffraction data from several microcrystals. The enantioselective adsorption of 2-butanol is demonstrated over the high-silica, enantioenriched STW-type molecular sieve.