Reactivity of surface species on zeolites in methanol conversion

The surface species formed by the interaction of methanol with HY and HZSM-5 zeolites modified with nonskeletal Al were examined using FT-IR spectroscopy and temperature-programmed desorption accompanied by conversion of preadsorbed methanol with mass spectrometric detection of the products evolved. Physisorbed methanol perturbed by various surface sites, methylcarboxonium ions, skeletal methoxyls , methoxyls on nonskeletal aluminium AlnO(CH3), and methoxyls substituting for silanol groups were found on both zeolite types. Their occurrence depended on the zeolite composition and the reaction temperature. The role of skeletal methoxyls and AlnOCH3 in the methanol conversion is discussed. In addition to the reaction of preadsorbed methanol the conversion over ZSM-5 catalysts under on-stream conditions was found to be sensitive to the presence of nonskeletal Aln.