Hydrogen Uptake on Coordinatively Unsaturated Metal Sites in VSB-5: Strong Binding Affinity Leading to High-Temperature D2/H2 Selectivity.

We examine the adsorption of hydrogen and deuterium into the nanoporous nickel phosphate, VSB-5. On the basis of gas sorption analysis, VSB-5 exhibits one of the highest measured H2 heats of adsorption (HOA) for hydrogen (16 kJ/mol) yet reported. This high HOA is consistent with an unusually large red shift in the Q(1) and Q(0) hydrogen vibrational modes as measured with in situ infrared spectroscopy. The HOA for D2 is measured to be 2 kJ/mol higher than that for H2. "Ideal adsorbed solution theory" analysis of H2 and D2 isotherms provides selectivities above 4 for deuterium at 140 K, suggesting that VSB-5 is a promising adsorbent for pressure-swing adsorption-type separations of hydrogen isotopes.