Structure and 3D-3D Topotactic Transformation of the Aluminophosphate Molecular Sieve PST-5 and Its Implication in New Zeolite Structure Generation

Zeolites have attracted great interest over recent decades. Their unique pore structures of molecular dimensions and tunable compositions make them ideal for shape selective catalysis and separation. However, targeted synthesis of zeolites with new pore structures and compositions remains a key challenge. Here, we propose a novel approach based on a unique 3D-3D topotactic transformation, which takes advantage of weak bonding in zeolites. This is inspired by the structure transformation of PST-5, a new aluminophosphate molecular sieve, to PST-6 by calcination at 500 °C. The structure of PST-5 was determined from micrometer-sized crystals by 3D electron diffraction (3DED, also known as MicroED). We found that the 3D-3D topotactic transformation involves two types of building units where penta- or hexa-coordinated Al is present. We applied this approach to several other zeolite systems and predicted a series of new zeolite structures that would be synthetically feasible. This method provides a new concept for the synthesis of targeted zeolites, especially those which may not be feasible by conventional methods.