NMR Spectroscopic and Theoretical Analysis of Boron Incorporation into the AlPO-41 Framework Facilitated by Silicon

Abstract

The introduction of boron into the aluminophosphate AlPO-41 framework (AFO structure), enhanced by the presence of silicon, was investigated using solid-state NMR spectroscopy and DFT calculations. While boron incorporation into the pure AlPO-41 was negligible, simultaneous co-substitution with silicon facilitated the stabilization of tetrahedral boron within the framework, as evidenced by ¹¹B solid-state NMR. ²⁹Si NMR revealed a more uniform silicon distribution in BSAPO-41 compared to SAPO-41, with isolated Si(4Al) sites and silicon patches identified. The theoretical modeling suggested preferential substitution sites for Si and B. These findings highlight the synergistic role of silicon in enabling boron incorporation, offering a pathway to fine-tune the acidity and catalytic properties of aluminophosphate molecular sieves. Additionally, the theoretical modeling allowed to establish the mechanism of hydration of AlPO-41.