Structure and Kinetic Selectivity of Trapdoor Zeolites in Hydrogen Isotope Separation

The potential of two families of trapdoor zeolites with chabazite (CHA) and merlinoite (MER) structures have been explored for selective hydrogen isotope separation by investigating the influence of framework structure and the presence of different trapdoor cations (K+, Rb+, and Cs+) on the thermal and kinetic responses. By leveraging the distinct porous structures of these frameworks, the separation of H2 and D2 gases is facilitated. The energy required for hydrogen to displace the door-keeping cations and fully access the inner zeolite porosities is identified for each sample, with frameworks containing heavier cations requiring higher critical temperatures. At 77 K, both MER and CHA frameworks show D2 adsorption amounts nearly double those of H2. Kinetic studies indicate slower diffusion for D2 molecules through these porous structures compared to H2, particularly at pressures below 100 mbar. This research suggests that D2 is more likely to access a broader range of diffusion pathways than H2, due to the presence of the trapdoor cations restricting certain pathways during gas sorption. This leads to differing kinetic responses, increased adsorption amounts and prolonged equilibration times for D2, indicating potential for effective separation of H2 and D2 using the molecular trapdoor mechanism.