The aluminosilicate ZSM-5 and silicalite-1, a high silicate zeolite, have attracted considerable recent interest due to their wide applicability as shape-selective catalysts and adsorbents. Many aromatic sorbate-ZSM-5 and sorbate-silicalite-1 structures have been investigated by single-crystal X-ray diffraction (van Koningsveld, Tuinstra, van Bekkum & Jansen, 1989
; Reck et al.
; van Koningsveld, Jansen & de Man, 1996
; van Koningsveld, Jansen & van Bekkum, 1996
; Nishi et al.
). However, the benzene-ZSM-5 and benzene-silicalite-1 structures have not yet been determined by single-crystal X-ray diffraction.
ZSM-5 and silicalite-1, both MFI (IUPAC code of this family) zeolites, undergo many phase transitions with calcinations or adsorption, as summarized in Fig. 1. A model of these phase transitions is shown in Fig. 2. Initially, the orthorhombic crystal phase of as-synthesized tetrapropylammonium (TPA)-MFI zeolite transforms into monoclinic twin phases after calcination. The monoclinic twin crystal, H-ZSM-5, exhibits a reversible phase transition to a single-crystal orthorhombic phase at ~ 340 K (van Koningsveld, Jansen & van Bekkum, 1987
). On the other hand, van Konigsveld et al.
obtained a single crystal of monoclinic ZSM-5 after applying uniaxial mechanical stress that altered the populations of the monoclinic twin domains (van Koningsveld, Tuinstra, Jansen & van Bekkum, 1989
). They also analyzed the single-crystal structure of monoclinic ZSM-5 (van Koningsveld, Jansen & van Bekkum, 1990
). The authors recently developed a simple method for preparing monoclinic single crystals of ZSM-5 and determining the monoclinic structure of ZSM-5 (Kamiya et al.
). Generally, monoclinic twin MFI crystals transform into orthorhombic sorbate-MFI single crystals after adsorbing aromatic compounds other than benzene. However, after adsorbing benzene or chain compounds, the crystals remain in the monoclinic twin phase, so the structures of benzene-ZSM-5 and benzene-silicalite-1 remain unclear.
Phase transitions of MFI zeolite.
Model of the phase transitions of MFI zeolite.
In this report the authors present a new method of obtaining single crystals of benzene-silicalite-1, and describe its structure, which was determined for the first time by a single-crystal method.