H2/D2 adsorption and desorption studies on carbon molecular sieves with different pore structures

The critical effect of confinement on the interaction of hydrogen isotopes (H2 and D2) with carbon surfaces was investigated through a combined low temperature adsorption/thermal desorption spectroscopy (TDS) study on three carbon molecular sieves (CMS) possessing nanopores with nominal sizes between 0.3 and 0.5 nm. The porous structure and the sorption properties of all three adsorbents were characterized by N2 (77 K) and CO2 (273 K), as well as H2 and D2 (77 K) low pressure (up to 1 bar) adsorption measurements. The interaction of the carbons with hydrogen, deuterium, and an isotopic H2/D2 gas mixture was further studied by means of TDS measurements, extended to temperatures down to 20 K. The differences in the H2/D2 adsorption/desorption profiles of the three CMS samples are correlated with the respective micropore size distributions. The presence of very narrow micropores, with size close to the kinetic diameter of the hydrogen molecule, resulted in enhanced hydrogen (both for H2 and D2) interactions, giving rise to a TDS maximum centered on 122 K, the highest desorption temperature ever measured for the desorption of physisorbed hydrogen. Furthermore, the quantum effects on hydrogen/deuterium adsorption on CMS adsorbents have been addressed for the first time using the TDS technique.