Adsorption

, Volume 2, Issue 1, pp 9–21 | Cite as

The effect of nanopore shape on the structure and isotherms of adsorbed fluids

  • D. Keffer
  • H. Ted Davis
  • Alon V. McCormick
Article

Abstract

A Grand Canonical Monte Carlo simulation method is used to determine the adsorption isotherms, interaction energies, entropies, and density distribution of a Lennard-Jones fluid adsorbed in smooth-walled nanopores of varying size and shape. We specifically include very crowded pores, where packing effects are important. Differences in the isotherms of slit, cylindrical, and spherical nanopores of varying sizes can be explained in terms of the adsorbate-adsorbate interaction energy, the adsorbate-pore interaction energy, and the density profiles, which influence the balance between the former and the latter energy contributions. The expectation from low loading studies that the most energetically favorable adsorbate-pore interactions maximize adsorption is not borne out at intermediate and higher loadings. Instead, the relationships between adsorbed amounts and pore size and shape are found to be strong functions of the depth and steepness of the external potential, the extent to which adsorbate-adsorbate repulsion establishes short range fluid order, and the accessible pore volume. This study has implications for high pore density processes in nanoporous materials, such as zeolite catalysis, separations, and templating in zeolite synthesis.

Keywords

nanopores zeolites Monte Carlo simulations 

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References

  1. Allen, M.P. and D.J. Tildesley, Computer Simulation of Liquids, Oxford University Press, Oxford, 1987.Google Scholar
  2. Antonchenko, V.Y., V.V. Ilyin, N.N. Makovsky, and V.M. Khryapa, “Short-range Order in Cylindrical liquid-filled Micropores,” Mol. Phys., 65, 1171–83 (1988).Google Scholar
  3. Bratko, D., L. Blum, and M.S. Wertheim, “Structure of Hard Sphere Fluids in Narrow Cylindrical Pores,” J. Chem. Phys., 90, 2752–57 (1989).Google Scholar
  4. Carignan, Y.P., T. Vladimiroff, and A.K. Macpherson, “Molecular Dynamics of Hard Spheres. III. Hard Spheres in an almost Spherical Container,” J. Chem. Phys., 88, 4448–50 (1988).Google Scholar
  5. Davis, H.T., Statistical Mechanics of Phases, Interfaces, and Thin Films, VCH, Weinheim, 1995.Google Scholar
  6. Demi, T., “Molecular Dynamics Studies of Adsorption and Transport in Micropores of Different Geometries,” J. Chem. Phys., 95, 9242–47 (1991).Google Scholar
  7. Derouane, E.G., J.M. Andre, and A.A. Lucas, “Surface Curvature Effects in Physisorption and Catalysis by Microporous Solids and Molecular Sieves,” J. Cat., 110, 58–73 (1988).Google Scholar
  8. Dunne, J. and A.L. Myers, “Adsorption of Gas Mixtures in Micropores: Effect of Difference in size of Adsorbate Molecules,” Chem. Eng. Sci., 49, 2941–2951 (1994).Google Scholar
  9. Glandt, E.D., “Density Distribution of Hard-Spherical Molecules inside Small Pores of Various Shapes,” J. Col. Inter. Sci., 77, 512–24 (1980).Google Scholar
  10. Groot, R.D., N.M. Faber, and J.P. van der Eerden, “Hard Sphere Fluids near a Hard Wall and a Hard Cylinder,” Mol. Phys., 62, 861–74 (1987).Google Scholar
  11. Han, K.K., J.H. Cushman, and D.J. Diestler, “Grand Canonical Monte Carlo Simulations of a Stockmayer Fluid in a Slit Micropore,” Mol. Phys., 79, 537–45 (1993).Google Scholar
  12. Heinbuch, U. and J. Fischer, “Liquid Argon in a Cylindrical Carbon Pore: Molecular Dynamics and Born-Green-Yvon Results,” Chem. Phys. Let., 135, 587–90 (1987).Google Scholar
  13. Jiang, S., C.I. Rhykerd, and K.E. Gubbins, “Layering, Freezing Transitions, Capillary Condensation, and Diffusion of Methane in Slit Carbon Pores,” Mol. Phys., 79, 373–91 (1993).Google Scholar
  14. Macelroy, J.M.D. and S.H. Suh, “Computer Simulation of Moderately Dense Hard-Sphere Fluids and Mixtures in Microcapillaries,” Mol. Phys., 60, 475–501 (1987).Google Scholar
  15. Macelroy, J.M.D. and S.H. Sub, “Simulation Studies of a Lennard-Jones Liquid In Micropores,” Mol. Sim., 2, 313–351 (1989).Google Scholar
  16. Macpherson, A.K., Y.P. Carignan, and T. Vladimiroff, “Molecular Dynamics of Hard Spheres. II. Hard Spheres in a Spherical Cavity,” J. Chem. Phys., 87, 1768–70 (1987).Google Scholar
  17. Murad, S., P. Ravi, and J.G. Powles, “A Computer Simulation Study of Fluids in Model Slit, Tubular, and Cubic Micropores,” J. Chem. Phys., 98, 9771–81 (1993).Google Scholar
  18. Peterson, B.K., J.P.R.B. Walton, and K.E. Gubbins, “Fluid Behaviour in Narrow Pores,” J. Chem. Soc., Faraday Trans. 2, 82, 1789–1800 (1986).Google Scholar
  19. Peterson B.K. and K.E. Gubbins, “Phase Transitions in a Cylindrical Pore: Grand Canonical Monte Carlo, Mean Field Theory, and the Kelvin Equation,” Mol. Phys., 62, 215–26 (1987).Google Scholar
  20. Saito, A. and H.C. Foley, “Curvature and Parametric Sensitivity in Models for Adsorption in Micropores,” AIChE J., 37, 429–36 (1990).Google Scholar
  21. Sarman, S., “The Influence of the Fluid-Wall Interaction Potential on the Structure of a Simple Fluid in a Narrow Slit,” J. Chem. Phys., 92, 4447–55 (1990).Google Scholar
  22. Schoen, M., C.L. Rhykerd, J.H. Cushman, and D.J. Diestler, “Slit-pore Sorption Isotherms by the Grand-Canonical Monte Carlo Method: Manifestations of Hysteresis,” Mol. Phys., 66, 1171–87 (1989).Google Scholar
  23. Somers, S.A. and H.T. Davis, “Microscopic Dynamics of Fluids Confined between Smooth and Atomically Structured Solid Surfaces,” J. Chem. Phys., 96, 5389–407 (1992).Google Scholar
  24. Somers, S.A., A.V. McCormick, and H.T. Davis, “Superselectivity and Solvation Forces of a Two Component Fluid Adsorbed in Nanopores,” J Chem. Phys., 99, 9890–8 (1993).Google Scholar
  25. Tan, Z. and K.E. Gubbins, “Selective Adsorption of Simple Mixtures in Slit Pores: A Model of Methane-Ethane Mixtures in Carbon,” J. Phys. Chem., 96, 845–54 (1992).Google Scholar
  26. Van Tassel, P.R., H.T. Davis, and A.V. McCormick, “Open-system Monte Carlo simulations of Xe in NaA,” J. Chem. Phys., 98, 8919–28 (1993).Google Scholar
  27. Walton, J.P.R.B. and N. Quirke, “Capillary Condensation: A Molecular Simulation Study,” Mol. Sim., 2, 361–91 (1989).Google Scholar

Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • D. Keffer
    • 1
  • H. Ted Davis
    • 1
  • Alon V. McCormick
    • 1
  1. 1.Department of Chemical Engineering and Materials ScienceUniversity of MinnesotaMinneapolis

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