SOME PROPERTIES OF SURFACE METHOXY GROUPS AND OF ADSORBED METHYL-IODIDE ON ZEOLITES STUDIED BY C-13 NMR

Methyl groups created by the heterolytic scission of methyl iodide on alkaline or superacid forms of zeolites react chemically with nucleophilic lattice oxygen of the zeolitic structures. The surface bonded methyl (surface methoxyl) exhibits a shielding tenser of the carbon nucleus with a cylindrical symmetry, as follows from the shape of the broad line of the static powder spectrum. A single pulse C-13 MAS NMR spectrum without proton decoupling of methyl iodide on NaX zeolite yields a symmetric multiplet structure (quartet) of the signal for physically adsorbed methyl iodide, and a non-symmetric quartet for the splitted signal of the chemisorbed methyl at the lattice oxygen. The non-symmetry of this Line is explained by the anisotropy of the rotational movement of the methyl. Isotropic values of the chemical shift of the surface methoxyls, obtained from C-13 CPMAS NMR experiments on different zeolites, fit well the correlation line of the signals on the equalized electronegativity of the lattice oxygen.