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The feasibility of the sodalite-type (SOD) structures, Si 6 O 12 :(all–Si), Na 3 Si 3 Al 3 O 12 :(Na–AlSi(3:3)), Al 3 P 3 O 12 :(AlP(3:3)), and Ge 6 O 12 :(all–Ge), as hydrogen storage media is assessed by calculating the hydrogen uptake isotherms by means of grand canonical Monte Carlo (GCMC) calculations for the range 73–773 K and 0–3000 bars. The calculated uptakes are compared to experimentally measured values at 573 K and 100 bars and show a good quantitative agreement. Additionally, the isotherms show a good qualitative agreement to experimentally determined H 2 isotherms at 77 K in other small pore zeolites, thus further proving the strength of the employed methodology. The isotherms are then fitted with Dubinin–Astakhov (DA) and Henry’s isotherms to give the isosteric heats of adsorption Q st , by means of Clausius/Clapeyron, and the micropore volumes of each SOD-type. These Q st values are compared to results we obtained previously in a molecular mechanics (MM) study and to the Q st values extracted directly from the GCMC simulation, showing good agreement. The predicted maximum storage capacities, however, follow a different trend than the ones predicted by MM, because of the assumption of a rigid framework in the DA model; an assumption only valid for loadings smaller than ∼2.5 wt%. At technically interesting loading conditions, 573 K and 100 bar, a storage capacity of around 0.1 wt% is expected for each SOD-type. This lies far below the required capacity for a technically feasible H 2 storage medium. The more technologically interesting capacities of >4 wt% are found only to be achieved under extremely low temperature and/or extremely high pressure conditions. |
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