High-Silica,\nEnantiomerically Enriched STW-Type Molecular\nSieves

Enantiomerically enriched molecular sieves can provide\nnew opportunities\nfor enantioselective catalysis and adsorption. The potential of using\nthese materials for practical applications relies on the preparation\nof stable materials that can survive the rigors of use and regeneration.\nReported enantiomerically enriched STW-type molecular sieves contain\nlarge amounts of Ge that limit the structural stability. Higher Si-containing\nSTW-type molecular sieves will have enhanced stability, which should\nenable practical application. To achieve high-silica framework composition\nwithin enantiomerically enriched STW-type molecular sieves, a chiral\norganic structure-directing agent (OSDA) is computationally designed\nbased on predicted stabilization energy toward the STW framework that\nis superior to previously employed OSDAs. With enantiopure forms of\nthe designed OSDA, the synthesis of enantiomerically enriched STW-type\ngermanosilicate molecular sieves with the framework Si/Ge as high\nas 18 is achieved. This high-silica STW-type molecular sieve has a\nsignificantly higher Si framework composition from the previously\nreported enantiomerically enriched germanium-rich STW-type molecular\nsieve and exhibits stability upon thermal treatment to 800 °C.\nThe absolute stereochemistry of the framework structure is characterized\nby the dynamical refinement of microcrystal electron diffraction data\nfrom several microcrystals. The enantioselective adsorption of 2-butanol\nis demonstrated over the high-silica, enantioenriched STW-type molecular\nsieve.