Bronsted/Lewis Acid Sites Synergy in H-MCM-22 Zeolite Studied by 1H and 27Al DQ-MAS NMR Spectroscopy

Bronsted/Lewis acid sites synergy in H-MCM-22 zeolite was studied by solid-state nuclear magnetic resonance (NMR). Two-dimensional H-1 double quantum-magic angle spinning (DQ-MAS) NMR revealed the details of the spatial relationship between the Lewis and the Bronsted acid sites in a dealuminated H-MCM-22 zeolite, which implied the existence of a Bronsted/Lewis acid sites synergy. Two-dimensional Al-27 DQ-MAS NMR was used to give the details of the spatial proximities of various aluminum species. The Bronsted/Lewis acid sites synergy occurred in the supercage of the H-MCM-22 zeolite between a T-6 site Al and extra-framework Al species. C-13 CP/MAS NMR of adsorbed acetone demonstrated that the spatial proximities of the Bronsted and Lewis acid sites led to a synergy that enhanced the Bronsted acid strength of the dealuminated zeolites. H-1 MAS NMR of adsorbed deuterated pyridine confirmed that the Bronsted/Lewis acid sites synergy occurred in the supercage of H-MCM-22. This finding is important for understanding the mechanism of acid-catalyzed reactions on H-MCM-22 zeolites.