DNL-17: A Small-Pore Aluminophosphate in ABC-6 Family with 24 Stacking Layers Unraveled by Three-Dimensional Electron Diffraction.

Abstract

Small-pore aluminophosphate (AlPO) molecular sieves (MSs), particularly those in the ABC-6 family, have gained significant attention for their unique capabilities in selective adsorption and energy storage. However, developing new synthesis strategies for designing AlPOs with three-dimensional (3D) channel systems and determining the structures of nanosized novel AlPO MSs remain challenging tasks. In this study, we introduce a new small-pore AlPO with a 3D channel system, named DNL-17, synthesized by using a diquaternary ammonium compound as an organic structure-directing agent (OSDA). Its crystallographic structure was determined through advanced 3D electron diffraction (ED) techniques and further confirmed by emerging integrated differential phase contrast imaging. DNL-17 exhibits a remarkable 24-layer stacking sequence along the c-axis and features a variety of composite building units (CBUs), including d6r, can, cha, and eri. Significantly, a combination of 3D ED, theoretical calculations, and solid-state ¹³C NMR reveals that the employed OSDA adopts distinct conformations to stabilize different cages. This finding highlights a novel strategy for constructing AlPO MSs with diverse cage-based CBUs. Furthermore, DNL-17 demonstrates unique selective adsorption properties, particularly in the separation of n-butane and isobutane.