Adsorptions of methane and ethane molecules on silanol covered silicalite-1 (010) surface : AB initio fitted potential

Abstract

The interaction profiles between guest molecules, methane and ethane, and the silanol covered (010) silicalite-1 surface have been investigated using quantum ab initio, ONIOM (MP2/6-31G(d):HF/6-31G(d)) method including the correction due to the basis set super position error (BSSE). The silicalite-1 (010) surface, which perpendicular to the straight channel was selected and cut from an idealized MFI crystal lattice. The silanol groups on the surface were generated by adding hydrogen atoms to the broken -Si-O- bonds. The ONIOM energy data were fitted to an analytical function. Quality of the fitted function was, then, examined. The energetic data obtained from the two sources, ONIOM and fitted function, are in good agreement for both methane/silicalite-1 and ethane/silicalite-1 systems. It was also found that the optimal path for guest molecule to enter the straight channel is that at the center of the channel. The optimal orientation for methane is to point one H atom at the center and perpendicular to the surface leading to the binding energy of -5.75 kJ/mol. The corresponding energy for ethane is -10.92 kJ/mol in the configuration where the C-C bond points toward and perpendicular to the surface. The fitted potential function was examined by Thompho’s Ph.D. thesis using molecular dynamics (MD) simulations in order to validate the fitted functions, Reliability of the functions was clearly yielded.