SI-29 AND AI-27 MAS NMR-STUDY OF ZEOLITE BETA WITH DIFFERENT SI/AL RATIOS

29Si and 27Al MAS NMR and IR spectroscopies have been used to characterize zeolites-β covering a wide range of Si/Al ratios (7.6-110) and to analyze the dealumination process produced during calcination of TEA- or NH4-exchanged samples. The analyses of samples with low Si/Al ratio has permitted us to differentiate three types of structural sites and to detect some preferential occupation by Al of these sites. In dealuminated samples two new lines associated with SiOH have been identified in 29Si NMR spectra, the first assigned to structural sites, part of them occupied by Al in the starting zeolite, and the second associated with the amorphous material produced during calcination. © 1990.