Characterization of basic guest compounds on solid catalysts by 13C CP/MAS NMR spectroscopy of surface methoxy groups

Silica gel, dealuminated zeolite USY and cesium-exchanged zeolite Y were impregnated with alkali metal hydroxides or acetates followed by calcination. Surface methoxy groups formed upon loading these samples with methyl iodide were applied as C-13 NMR spectroscopic probes to investigate the formation of well dispersed basic guest compounds. The variation of the isotropic C-13 NMR shifts of methoxy groups bound to different guest compounds on silica gel (49.6-48.7 ppm) shows the same tendency as the electronegativities of alkali metal atoms introduced by impregnation. C-13 CP/MAS NMR studies of surface methoxy groups bound to guest compounds on silica gel and zeolites Y revealed an influence of the support on the C-13 chemical shift tensor. The application of this NMR spectroscopic method on cesium-exchanged zeolite Y impregnated with cesium hydroxide allows one to distinguish at least two types of oxidic guest compounds. Copyright (C) 1999 John Wiley & Sons, Ltd.