Abstract
Zeolites have unique pore structures of molecular dimensions and tunable compositions, making 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 an 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. The structure of nano-sized PST-5 crystals is determined by 3D electron diffraction. We find that the 3D-3D topotactic transformation involves two types of building units where penta- or hexa-coordinated Al is present. We apply this approach to several other zeolite systems and predict a series of new zeolite structures that would be synthetically feasible. This method provides a concept for the synthesis of targeted zeolites, especially those which may not be feasible by conventional methods.
Highlights
Zeolites have unique pore structures of molecular dimensions and tunable compositions, making them ideal for shape selective catalysis and separation
To confirm the model and obtain more accurate positions and atomic displace parameters (ADPs) of individual atoms, the model was further refined against the continuous rotation electron diffraction (cRED) data (Supplementary Table 2)
The structure model obtained by Rietveld refinement against synchrotron powder Xray diffraction (PXRD) data agrees well with that obtained from cRED data, which further confirms the framework structure of PST-5
Summary
Zeolites have unique pore structures of molecular dimensions and tunable compositions, making them ideal for shape selective catalysis and separation. We propose an 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. We find that the 3D-3D topotactic transformation involves two types of building units where penta- or hexacoordinated Al is present We apply this approach to several other zeolite systems and predict a series of new zeolite structures that would be synthetically feasible. Besides the conventional hydro-/solvothermal synthesis, several new synthetic strategies have been proposed for targeted zeolite synthesis These include bottom-up approaches that use, for example, pre-designed organic structure-directing agents (OSDAs)[14,15,16,17] and promotion of specific cavities as in the synthesis of embedded isoreticular zeolites[18,19], and top-down approaches, i.e., topotactic transformations. Solid-state nuclear magnetic resonance (NMR) spectroscopy indicated the presence of bridging hydroxyl groups in PST-5
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