Abstract

This study utilizes advanced solid-state NMR spectroscopy to elucidate the spatial distribution, coordination behavior, and inter-nuclear interactions of boron species in B-MFI zeolites. Through 13C-{11B} symmetry-based resonance-echo saturation-pulse double-resonance (S-RESPDOR) NMR experiment, we reveal that boron incorporation is preferentially directed by tetrapropylammonium (TPA+) structure-directing agents, with boron predominantly occupying both sinusoidal and straight channels rather than channel intersections. Quantitative analysis further indicates a closer proximity to terminal methyl groups of TPA+ in sinusoidal channels (B-Cγ′: ca. 2.8 Å) (1 Å=0.1 nm) compared to straight channels (B-Cγ: ca. 3.1 Å). Upon dehydration, two-dimensional (2D) 11B multiple-quantum magic-angle spinning (MQMAS) NMR, together with a 2D 1H-{11B} dipolar-based heteronuclear multiple quantum correlation (D-HMQC) experiment, identifies two distinct trigonal boron species, attributed to framework boron perturbed by proximal silanols, highlighting microenvironmental heterogeneity. Our findings establish that boron siting is template-directed and that dehydration induces distinct speciation, providing atomic-scale insights that are crucial for the rational design of zeolites.

文章链接：https://link.springer.com/article/10.1007/s40242-025-5137-2