Accelerated Crystallization of Zeolites via Solid Boron Free Radicals

The highly efficient synthesis of titanium silicate-1 (TS-1) zeolite remains a challenge. In this work, solid boron free radicals within hexagonal boron nitride (h-BN) were employed to accelerate the crystallization of TS-1. With the introduction of h-BN (1-10 wt % of SiO₂) into the traditional hydrothermal synthesis system, TS-1 zeolite can be obtained within 6-24 h with yields of 90-96%. The geometric matching between h-BN layered structure and the TS-1 crystal plane was observed by both TEM analysis and theoretical modeling, while solid-state free radicals generated at the edges of h-BN with defects were evidenced by aberration-corrected transmission electron microscopy and EPR analysis. Ab initio molecular dynamics simulation further indicated that the free radicals in h-BN promoted the transformation of orthosilicic acid (H₄SiO₄) into metasilicic acid (H₂SiO₃) with a negative LUMO, which is beneficial for the rapid dimerization reaction as the zeolite structural species. The resulting TS-1 zeolite then bonded with the h-BN as h-BN/TS-1 heterostructure, which exhibited enhanced catalytic performance for the propane dehydrogenation reaction, while the promotion mechanism was revealed by time-dependent density functional theory. This work developed an effective strategy to accelerate zeolite production with the assistance of solid free radicals, while providing a molecular-level understanding of the synthesis process.