Research Highlights

Synthesis of Novel Zeolites

2018-05-04 115


The unmistakable whistle you hear when boiling a kettle of water is a staple of many morning rituals throughout the world: heat water and steam will rise out as it comes to boil. Now, imagine heating a rock on your stovetop. You certainly would not expect the same thing to happen—unless it is a special kind of rock called zeolite.

From the Greek word zeo, meaning ‘to boil’ and lithos, meaning ‘stone,’ zeolites are microporous aluminosilicate minerals that can trap other molecules inside it. In other words, they are stable solids with a relatively open, three-dimensional crystal structures that can selectively absorb and trap molecules—such as water—that pass through their regular pores of fixed size. Zeolites can also be synthetically manufactured in precise and uniform sizes to suit particular applications—from water softeners and odor control to nuclear waste cleanup and petrochemical catalysts. Thus, the search for new zeolite structures is a crucial step for the betterment of our daily lives.

Collaborative research conducted by Professor Suk Bong Hong from the Division of Environmental Science and Engineering at POSTECH et al. has discovered PST-13 (POSTECH number 13), a new aluminophosphate, and from it, successfully synthesized PST-14: a small-pore molecular sieve with a zeolite topology made up of enantiomeric tetrahedral units, a feature never before observed in zeolite structural chemistry. This achievement was published in the world-renowned Angewandte Chemie as a Very Important Paper.

The team synthesized PST-13 by using diethylamine, one of the simplest organic amines, as an organic structure-directing agent. Through calcination, they were then able to transform PST-13 into its tetrahedral counterpart, PST-14. The team used continuous rotation electron diffraction (cRED) data to solve and refine their structures, which were further confirmed and refined by Rietveld analysis of synchrotron powder X-ray diffraction (XRD) data. The structure of both zeolites consist ‘nonjointly’ of chiral pairs of previously undiscovered 1,5- and 1,6-open double 4-rings. The novel chirality of the structures is of particular interest because of the prospective potentiality in research and applications in the field.

Accordingly, the team generated 13 new hypothetical structures based on the discovery and also demonstrated their chemical feasibility and synthesizability. Prof. Hong expressed his enthusiasm and anticipation in the potential myriad applications of the new zeolites, of which the PST-14 will be forwarded to the International Zeolite Association for registration with a three-digit IZA code (POR).

This research was supported by the National Creative Research Initiative Program through the National Research Foundation of Korea, the Swedish Research Council (VR), and the Knut and Alice Wallenberg Foundation through the project grant 3DEM-NATUR.