STUDY OF SORBENT SORBATE INTERACTIONS IN SOME AROMATICS SILICALITE SYSTEMS BY USE OF NUCLEAR-MAGNETIC-RESONANCE WITH CROSS-POLARIZATION

The solids obtained by loading silicalite (a highly dealuminated silic eous ZSM-5 material) with up to four molecules/uc of aromatics (benzen e, p-xylene, p-dichlorobenzene, naphthalene) were studied by Si-29 HP- MAS and CP-MAS NMR. Cross-polarization (CP) gives informations on the possible locations and orientation of the sorbate molecules in the act ive sites of the zeolite. In agreement with structural investigations (X-ray and neutron powder diffraction), it is shown that all four sorb ate molecules are located at the channel-intersections (site I) : p-xy lene, p-dichlorobenzene and naphthalene present the same orientation, whereas benzene presents several orientations.