Because of its relatively large and tunable pore sizes, mesoporous silicas are good candidates as catalyst supports in the production of biofuels. Understanding the transport properties of a material like SBA-15 with its secondary pore network of meso- and micro-pores is important in engineering useful catalyst systems. Contrast-matching small-angle neutron scattering (CM-SANS) studies showed that the SBA-15 micropore structure1 is consistent with cylindrical pores with an onset diameter of ~5.5 �. Quasi-elastic neutron scattering (QENS) data on methane in SBA-15 contains information about rotational and translation diffusivity in the pore network2 but can be hard to interpret because diffusion rate depends on pore size, temperature, and degree of filling. Here we present a simulation of pore filling of SBA-15 as a function of pressure at 77K. We follow a formulation of Rasaiah and coworkers3 to determine the chemical potential of methane in different size pores and then construct probability distributions for methane filling in a network with a distribution of pore sizes. We discuss the use of molecular dynamics simulations for modeling the QENS data.References(1)    Pollock, R.A., et al, Chem. Mater. 2011, 23, 3828-3840.(2)    Pollock, R.A., Ph.D. Thesis, 2012, University of Maine.(3)    S. Vaitheeswaran, J. C. Rasaiah, and G. Hummer, JCP 121 (16), 7955 (2004).

Modeling the filling of methane in heterogeneous pore networks

248th National Meeting (2014)

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