Viability of hydrogen isotopes separation via heterolytic dissociation-driven Chemical Affinity Quantum Sieving on inexpensive alkali-earth oxides

The quest for economically viable strategies to separate hydrogen molecule isotopologues has recently provided clear indications on the design principles that ought to be implemented to satisfy the growing request for deuterium and tritium homodimers. In this respect, we investigate by electronic structure calculations whether easily obtainable, environmentally respectful, and inexpensive alkali-earth oxides may be suitable materials when it comes to separating hydrogen isotopologues. We found that hydrogen dimers heterolytically dissociate upon chemisorption on the most reactive three-coordinated vertex Mg, Ca, Sr and O sites, the formed species remaining in close proximity due to a strong H+/H– interaction. The inclusion of quantum zero point motion in the description of the adsorption energetics, mandatory if one wishes to differentiate the isotopologues behavior, indicated that the chemisorption energy becomes more negative the heavier the isotope involved. Isotopic selectivities estimated via Ideal Adsorbed Solution Theory (IAST) appear orders of magnitude higher than those previously presented. As chemisorbed species may catalyze an exchange reaction with gaseous molecules hinging on their nature as Broensted acid and Lewis base, we searched for possible processes competing with the desorption of vicinal adsorbed species; our results suggest that production of heterodimers (e.g. HD) is unlikely.