Quantitatively Mapping the Distribution of Intrinsic Acid Sites in Mordenite Zeolite by High-Field ²³Na Solid-State Nuclear Magnetic Resonance

Abstract

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, 23 Na-27 Al D-HMQC was performed combined with high-field 23 Na MQ MAS NMR and DFT calculation, which provided an unambiguous attribution of the 23 Na chemical shifts and further helped to improve the resolution of 27 Al MAS NMR. By fitting the 23 Na and 1 H MAS NMR spectra of Na/H-MOR, the intrinsic BAS contents in different Tsites 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.

Cation-induced speciation of port-size during mordenite zeolite synthesis

“…S7 and Table S2 † ). Interestingly, Fan et al using 23 Na MAS NMR claimed to observe 3 sodium sites: I, IV & VI and assigned them to T3, T4 and T1+2 respectively, 43 however, we do not see any evidence of electron density around position VI (12-ring).…”

Enhancing the separation of C2H4/C2H6 in customized MOR zeolites

“…It is well known that the amount and distribution of cations are closely linked to those of the aluminum atoms. The spatial occupancy priority of Na + cations is 8-MR > SP > 12-MR, 43,45 which is crucial for customizing the adsorption properties of MOR to achieve a specific separation task. To ensure a fair comparison, the unit cell (U.C.)…”

Spatial Proximities between Brønsted Acid Sites, AlOH Groups, and Residual NH4+ Cations in Zeolites Mordenite and Ferrierite

“…23,59 The occupancy of the T3 position, which is located in the 8-ring pockets between [5 2 •8 3 ] and [4 2 •5 8 •8 2 ] cages, correlates with the activity of the carbonylation reaction of dimethylether. 60 The model discussions are restricted to NH 4…”

“…Two Al positions at T3 and T4 sites are considered among the four T sites of the mordenite structure. , The occupancy of the T3 position, which is located in the 8-ring pockets between [5 2 ·8 3 ] and [4 2 ·5 8 ·8 2 ] cages, correlates with the activity of the carbonylation reaction of dimethylether . The model discussions are restricted to NH 4 + and H + interactions because of the complex diversity of extra-framework moieties with AlOH groups …”