Characterization of basic guest compounds on solid catalysts by13C 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 13C NMR spectroscopic probes to investigate the formation of well dispersed basic guest compounds. The variation of the isotropic 13C 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. 13C 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 13C 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.