Suchergebnisse

[EN] The synthesis of crystalline molecular sieves with pore dimensions that fill the gap between microporous and mesoporous materials is a matter of fundamental and industrial interest(1-3). The preparation of zeolitic materials with extralarge pores and chiral frameworks would permit many new applications. Two important steps in this direction include the synthesis(4) of ITQ-33, a stable zeolite with 18 x 10 x 10 ring windows, and the synthesis(5) of SU-32, which has an intrinsically chiral zeolite structure and where each crystal exhibits only one handedness. Here we present a germanosilicate zeolite (ITQ-37) with extralarge 30-ring windows. Its structure was determined by combining selected area electron diffraction ( SAED) and powder X-ray diffraction (PXRD) in a charge-flipping algorithm(6). The framework follows the SrSi2 (srs) minimal net(7) and forms two unique cavities, each of which is connected to three other cavities to form a gyroidal channel system. These cavities comprise the enantiomorphous srs net of the framework. ITQ-37 is the first chiral zeolite with one single gyroidal channel. It has the lowest framework density (10.3 T atoms per 1,000 angstrom(3)) of all existing 4-coordinated crystalline oxide frameworks, and the pore volume of the corresponding silica polymorph would be 0.38 cm(3) g(-1). ; This project is supported by the CICYT ( Project MAT 2006-14274-C02-01 and Prometeo 2008 GV), the Swedish Research Council (VR) and the Swedish Governmental Agency for Innovation Systems (VINNOVA). J.S. and C. B. are supported by post-doctoral grants from the Carl-Trygger and Wenner-Gren foundations respectively. M. M. thanks ITQ for a scholarship. ; Sun, J.; Bonneau, C.; Cantin Sanz, A.; Corma Canós, A.; Díaz Cabañas, MJ.; Moliner Marin, M.; Zhang, D. (2009). ITQ-37 a chiral zeolite framework following the SrSi2 net and containing 30-ring extra-large gyroidal channels. Nature. 458(7242):1154-1158. https://doi.org/10.1038/nature07957 ; S ; 1154 ; 1158 ; 458 ; 7242 ; Davis, M. E. Ordered porous ...

[EN] It was found that either polymorph B or polymorph C of zeolite beta can be obtained from the same structure directing agent: 4,4-dimethyl-4-azonia-tricyclo[5.2.2.0(2,6)] undec-8-ene hydroxide. The synthesis occurs through a consecutive process where polymorph B is first formed and then transformed into polymorph C. It is possible to produce a zeolite highly enriched in polymorph B, provided that the transformation of this phase into polymorph C is slowed down up to the point where polymorph C is only detected at trace levels. The structure of polymorph B was determined for the first time by electron crystallography with SAED and HRTEM from areas of unfaulted polymorph B crystals. ; Financial support from the Spanish Government (Project MAT2006-14274-C02–01) and the EU Commission (TOPCOMBI Project) is gratefully acknowledged. M.M. thanks CSIC for an I3P grant. J.S. is supported by a postdoctoral grant from the Carl Trygger Foundation. The Berzelii Centre EXSELENT is supported by the Swedish Research Council (VR) and the Swedish Governmental Agency for Innovation Systems (VINNOVA). ; Corma Canós, A.; Moliner Marin, M.; Cantin Sanz, A.; Díaz Cabañas, MJ.; Jorda Moret, JL.; Zhang, D.; Sun, J. (2008). Synthesis and structure of polymorph B of zeolite Beta. Chemistry of Materials. 20(9):3218-3223. doi:10.1021/cm8002244 ; S ; 3218 ; 3223 ; 20 ; 9