CHARACTERIZATION OF GUEST MOLECULES SORBED IN ZEOLITES OF KNOWN STRUCTURE .6. LOCALIZATION OF METHANOL AT SEVERAL PORE FILLINGS IN A HIGHLY SILICEOUS MFI SILICALITE MATERIAL

Structural investigations on a silicalite/methanol (MeOH) system by X-Ray powder diffraction and Rietveld profile refinements show that there are six possible adsorption sites for the methanol molecules. Those located in the channel-intersection (sites I-III and I-III') or in the zig-zag channel sections (sites I-II and I-II') form dimeric entities (maximum 4MeOH/uc concentration for each of the corresponding four individual sorbate species) presenting intermolecular interactions comparable to those observed in the orthorhombic methanol crystal structure. The sorbed species in the straight-channel sections seem to be monomeric (maximum 2MeOH/uc concentrations for each of these two species). The highest theoretical pore-filling amounts to 2 0MeOH/uc, in good agreement with the experimentally observed value (almost-equal-to 1 9MeOH/uc). All the investigated silicalite/methanol complexes present the monoclinic P2(1)/n.1.1 framework symmetry, which is an indication that there are no sorbate/sorbate or sorbate/silicalite interaction in or through the straight-channel sections.