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 siliceous ZSM-5 material) with up to four molecules/uc of aromatics (benzene, 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 active sites of the zeolite. In agreement with structural investigations (X-ray and neutron powder diffraction), it is shown that all four sorbate molecules are located at the channel-intersections (site I) : p-xylene, p-dichlorobenzene and naphthalene present the same orientation, whereas benzene presents several orientations.