Abstract
The state of boron in the boron-modified mordenite has been investigated by 11B NMR and quantum chemical calculation. Two different kinds of boron species in tetrahedral coordination are clearly observed in the two-dimensional (2D) 11B triple-quantum (3Q) magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra. The signal at −3.1 ppm is due to the normal four-coordinated framework boron species, while that at 0.3 ppm is attributed to a new kind of four-coordinated framework boron species. The association of the new tetrahedral BO 4 unit with the framework of mordenite is confirmed using 11B{ 29Si} rotational echo double resonance (REDOR) experiment, and its detailed structure is determined by ab initio calculation, which suggests that the new tetrahedral BO 4 is connected to two hydroxyl groups, in the form of (OSi) 2B(OH) 2. The calculated isotropic 11B chemical shifts of the two tetrahedral boron species are in good agreement with the experimental values.
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