Collect. Czech. Chem. Commun. 2004, 69, 1537-1552

Bridging Methoxy Groups in NaY, NaX and NaLSX Zeolites

Vladimír Bosáčeka,*, Stanislav Vratislavb and Mája Dlouháb

a J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, 182 23 Prague 8, Czech Republic
b Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, 115 19 Prague 1, Czech Republic


Distribution of chemisorbed methyl groups and sodium cations in the structure of NaY, NaX and NaLSX zeolites was estimated by neutron diffraction. Chemisorbed methyl groups were prepared in the structure by reaction of methyl iodide with reactive sodium cations available in SII and SIII positions of faujasites. Methyl cations CH3+, formed in the reaction, react immediately with the lattice oxygen forming surface bonded methyl groups in bridging configuration. 13C NMR signals of chemisorbed surface species and their linear dependence on the intermediate electronegativity of the zeolite lie in the interval from 53 ppm for most basic CsLSX to 58 ppm TMS for stabilized and acid leached sample of H,NaY-St. Changes in the distribution of structural sodium cations in the lattice after chemisorption of methyl cations have been detected. C-O distances in surface methoxy groups in void cavities were longer than in ordinary crystalline organometallic compounds with bridging methoxy groups. The location of chemisorbed methyl groups at the O1 lattice oxygen type was most probable for NaY. Nuclear densities of chemisorbed methyl groups were detected in NaX at O1 and at O4 lattice oxygens. The origin of the split signal at 58 ppm on NaX and NaLSX samples has been discussed.

Keywords: Zeolites; Cations in faujasites; Chemisorbed methylium cations; Neutron diffraction; 13C MAS NMR spectroscopy.

References: 60 live references.