Role of hindered rotation in the physical adsorption of hydrogen weight and spin isomers

Theoretical estimate ofortho-paraseparation coefficients for H2and D2on A-type zeolites for small and medium coverage

“…The temperature dependence of the o-p separation coefficients for small coverage for the model zeolite 4A presented in figure 8 shows that there is reasonable agreement between theory and experiment [5] within temperture range 135-160 K and for ionicity q0 not exceeding 6.8. Generally, whatever factor might influence q0 in different models, o-p separation coefficients would grow with the increase of q0 due to the increasing interaction of the quadrupole moment of the adsorbate with the field of the ions.…”

“…Data on o-p separation coefficients obtained for small coverage [5] is more informative than that for high coverage, since the electrostatic fields of the ions are not screened by neighbouring molecules. This effect can be especially important for zeolite cavities with nearly spherical shapes.…”

“…for the separation of isotopic and spin modifications of dihydrogen [1][2][3][4][5][6][7]. Abundant experimental data have been thus far collected in this field.…”

Computational study of molecular hydrogen in zeolite Na-A. I. Potential energy surfaces and thermodynamic separation factors for ortho and para hydrogen

“…The listed uncertainties are the standard deviations from the mean values of S. Our uncertainties are dominated by the variation of S from place to place in the cavity, rather than by the expected error in a single measurement of S. ͑This is true despite the fact that uncertainties increase as the temperature decreases, and hence the range of positions visited by the hydrogen is reduced. The explanation may lie in the great sensitivity of the tunnel-splitting energy to the height of the hindering barrier.͒ For comparison with our data, we have listed the experimental results of Gant et al 61 Those results, taken during gassolid chromatography experiments in zeolite Na-A, were conducted in the temperature range 135-160 K. We have extrapolated these results where relevent, assuming a linear ͑Arrhenius͒ relationship between ln(S) and 1/T. From the experimental data, and on theoretical grounds, one would not expect this relationship to hold over a wide range of temperatures; indeed an extrapolation to Tϭ300 yields a nonphysical value of SϽ1, and is not listed in the table.…”

Adsorption and separation of hydrogen isotopes in carbon nanotubes: Multicomponent grand canonical Monte Carlo simulations

“…10,12 Separation of spin isomers ͑ortho-para͒ has also been observed experimentally and explained in terms of a model of a hindered quantum rotor. [13][14][15][16][17][18][19] The selectivities observed for adsorption of hydrogen isotopes on common sorbents such as activated carbons, zeolites, and alumina are typically in the range of 1.1-3. In contrast, our previous theoretical and simulation studies predict that adsorption of hydrogen isotopes in carbon nanotubes may result in extraordinarily large selectivities.…”