Flexibility of the MFI silicalite framework upon benzene adsorption at higher pore-fillings: A study by X-ray powder diffraction, NMR and molecular mechanics
- Univ. Claude-Bernard, Villeurbanne (France)
At higher pore fillings (n {ge} 4) the silicalite (SIL)/nbenzene(BENZ) solid state phase diagram is very complex. The crystal structures of the 4, 6, and 8 molecules/uc loaded stoichiometric benzenates are investigated by X-ray powder diffraction profile refinements (Rietveld method) and energy minimization calculations (Buckingham model). In SIL-4BENZ (monoclinic P2{sub 1}/n {center_dot} 1 {center_dot} 1, M symmetry), the benzene molecule is disordered and presents at least two distinct orientations centered near the channel intersections (sites 1). In SIL-6BENZ (orthorhombic P2{sub 1}2{sub 1}2{sub 1}, O2 symmetry), the two independent benzene molecules are located at the channel intersections (sites 1) and in the zigzag channels (sites 2); the benzene at site 1 might be disordered (several equi-probable orientations as in SIL-4BENZ). In the sorbate saturated SIL-8BENZ complex (orthorhombic Pnma, O1 symmetry) the two independent sorbate species are ordered and located at sites 1 and in the straight channels (sites 3). In SIL-6BENZ and SIL-8BENZ, the sorbate/sorbate interactions are comparable to those observed in crystalline benzene (T-association). Sorption of benzene in the MFI channels provokes a strong elliptical deformation of the pore openings. At benzene saturation, the MFI unit-cell parameters correspond to a pseudo-tetragonal deformation, but the framework symmetry remains orthorhombic O1.
- OSTI ID:
- 514719
- Journal Information:
- Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 7 Vol. 32; ISSN MRBUAC; ISSN 0025-5408
- Country of Publication:
- United States
- Language:
- English
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