International Journal of Quantum Chemistry
International Journal of Quantum Chemistry
4 years ago

Toward separation of hydrogen isotopologues by exploiting zero-point energy difference at strongly attractive adsorption site models

Toward separation of hydrogen isotopologues by exploiting zero-point energy difference at strongly attractive adsorption site models
Thomas Heine, Toshiki Wulf
Recent reports on hydrogen isotope separation in metal-organic frameworks are rationalized by the presence of undercoordinated metal sites. In this work, we screen undercoordinated divalent metals for their performance as hydrogen separating agents in common chemical environments (as free dications, as part of M2(HCOO)4 paddlewheels and in metal porphyrins). We calculate heat of adsorption and selectivity using the Langmuir model and the density-functional-based potential energy surface. Our calculations show a strong metal ion dependence of the adsorption energy in paddlewheels, but rather small impact of metal choice in stable porphyrins. D2-over-H2 selectivities reach top values of 12 for Co2+ paddlewheels, while only oxidatively unstable porphyrins incorporating Cr2+, V2+, and Ti2+ show high selectivities. Undercoordinated metal ions in porous materials act as isotopologue-selective hydrogen-affine sites. Density-functional theory in conjunction with anharmonic vibrational analysis of the degrees of freedom of H2 is used to screen divalent metal ions in M2(HCOO)4 paddlewheel and porphyrin model complexes for combinations with high D2-over-H2 selectivities to be investigated in future experimental studies.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/qua.25545

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