Potential parameters for helium adsorption in silicalite

The pore volume of a micro or a nanoporous material is one of the crucial parameters in molecular simulation of gas adsorption. It is necessary to compare the results of the simulations with that of the experiments. In simulations, the pore volume is usually obtained from the configuration integral using the potential parameters of helium–solid interactions. The state of the art in obtaining these helium–solid parameters is through Lorentz–Berthelot mixing rules, used in conjunction with potential parameters of another “adsorbing” gas. In such an approach, the parameters (and hence helium pore volume) depend on choice of the adsorbing gas. However, “true” helium pore volume in simulations can only be obtained by mimicking the experimental adsorption behavior of helium itself, without involving any other gas. In this work, we report a consistent method to obtain the potential parameters for helium adsorption on a porous solid from low pressure helium adsorption data. The method is applied to helium–silicalite system and the parameters for He–O interactions in silicalite were obtained to be 3.06 Å and 22.9 K. Using these parameters, a helium pore volume of 0.151 cm3/g (at 300 K) is obtained for silicalite. The results are further validated by comparing the adsorption isotherms of helium in the high pressure region.

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► A method to obtain helium–silicalite potential parameters from low pressure helium adsorption data is presented.
► The method does not require non-adsorbing helium assumption (at any temperature).
► The potential parameters are useful to describe adsorption behavior of helium in silicalite over a wide temperature and pressure range.