Study of methane adsorption in MFI and MEL zeolites by combination of the electronegativity equalization method and molecular dynamics

Characteristics of methane molecules adsorbed in MFI and MEL zeolites have been studied by a combination of the electronegativity equalization method and molecular dynamics (CIEEM MD, see preceding paper). The inclusion of polarization in the MD calculations is shown to reproduce important features of the host-guest interactions and gives additional information on the reactivity of the adsorbed species and on the active regions in the zeolite pore systems. The data obtained on the molecular electronegativity and the induced dipole moments indicate that the edges of the intersections of the channels are the active sites. The polarization of the methane molecules in the MEL structure is larger than that in MFI. This is largely related to the topology of the lattices. For the MFI structure the calculated dependence of the molecular dipole moment on the position of the molecules in the framework is in excellent agreement with the silicalite electrostatic potential obtained by periodical Hartree-Fock calculations (J. C. White and A. C. Hess, J. Phys. Chem., 1993, 97, 8703).