Quantitatively Mapping the Distribution of Intrinsic Acid Sites in Mordenite Zeolite by High-Field Na Solid-State Nuclear Magnetic Resonance.

It is of great significance to accurately quantify the Brønsted acid sites (BASs) at different positions of mordenite (MOR) zeolite. However, H-MOR obtained from Na-MOR can hardly avoid dealumination under hydrothermal conditions, which causes difficulty in the acid characterization. Herein, Na-Al -HMQC was performed combined with high-field Na MQ MAS NMR and DFT calculation, which provided an unambiguous attribution of the Na chemical shifts and further helped to improve the resolution of Al MAS NMR. By fitting the Na and H MAS NMR spectra of Na/H-MOR, the intrinsic BAS contents in different T-sites were measured by characterizing the location and content of sodium ions. These Na/H-MOR zeolites with various acid distributions were used for DME carbonylation and showed that the amount of BASs in the T3 site was proportional to the activity of carbonylation. This study provides a new method for investigating the intrinsic acid properties of zeolites.