Incorporation of Boron into the AlPO-11 Framework According to 11B and 27Al Solid-State NMR Spectroscopy and First-Principles Calculations

Abstract

Various aluminophosphates (AlPO-n) are a class of zeolite-like porous compounds built from alternating AlO₄ and PO₄ tetrahedra that demonstrate promising results as catalysts and catalyst supports. Their acid–base properties can be varied by substitution of different Al and P sites with different heteroatoms among which boron is of great interest. However, the ability to incorporate boron into the AlPO frameworks seems to be hindered since only very limited data are available on successful synthesis of BAPO (boron-substituted AlPO) materials. Here, we report the application of solid-state ²⁷Al, ¹¹B NMR techniques together with quantum chemical calculations for characterization of BAPO-11 obtained by hydrothermal synthesis. The coordination geometry of the B atoms in the framework is exclusively tetrahedral. However, the fraction of B atoms incorporated in the framework was very low and did not correspond to the B content in the initial composition. Extra-framework trigonal boron was also shown to be present in the sample. DFT calculations allowed us to suggest that boron replaced a small part of the Al1 site of the dehydrated AlPO-11 framework.