Probing influence of structure and temperature on H2 and D2 adsorption in trapdoor zeolites via neutron diffraction

Hydrogen and its heavier isotopes play essential roles in nuclear energy production. However, to obtain pure isotopes, conventional isotope separations rely on energy-intensive methods such as cryogenic distillation at temperatures ~20 K. To achieve separation under milder temperature conditions, physical adsorption using zeolites displaying a selective separation mechanism (so-called “trapdoor behaviour”) are favourable candidates. In these systems, deuterium (D2) can lower the energy barrier of the trapdoor cations, allowing D2 to move past the trapdoors into the internal pores of the zeolite, while other isotopes (such as protium, H2) are prevented from entering the internal cavities below a threshold trapdoor-opening temperature. Here we will investigate structural changes in two representative trapdoor zeolites (chabazite (CHA) and merlinoite (MER)) with different internal cavity structure, and cavity windows blocked by either Rb+ or Cs+ trapdoor cations. In-situ neutron diffraction on GEM is needed to detect structural breathing variations caused by the different interactions of these materials with H2 and D2 at room temperature and above the threshold gate opening temperature. These experiments will allow us to probe the different interactions of H2/D2 with these zeolite materials and will provide us with a better understanding of the potential of these materials for challenging and important isotope separations.