Formation of surface-bonded methoxy groups in the sorption of methanol and methyl iodide on zeolites studied by carbon-13 MAS NMR spectroscopy

Abstract

Methanol and methyl iodide as methylating agents react chemically with the surface atoms of zeolites and, under favorable conditions, yield surface-bonded methoxy groups. Zeolites with well-defined structures of faujasites, mordenites and ZSM5-containing various cations (Na + , Rb + , Mg 2+ , Ca 2+ ) and /or acid protons were investigated in chemisorption experiments using CH 3 I. The observed signals in the 53-59 ppm TMS region were assigned to the methoxy groups, i.e., methyl groups surface-bonded to the lattice oxygens. The chemical shift of these signals depends linearly on the equalized electronegativity of the oxygen of the given zeolite structure and becomes a measure of the lattice oxygen basicity (nucleophility)