Density Functional Investigation of Methanethiol and Dimethyl Sulfide Adsorption on Zeolite

Abstract

The density functional theory and cluster model methods have been employed to investigate the interactions between methanethiol, dimethyl sulfide and zeolites. The molecular complexes formed by adsorption of methanethiol or dimethyl sulfide on silanol H 3SiOSi(OH) 2OSiH 3 with five coordination forms or four coordination forms, and complexes formed by interactions of Brönsted acid sites of bridging hydroxyl H 3Si(OH)Al(OH) 2OSiH 3 with methanethiol or dimethyl sulfide have been investigated. Full optimization and frequency analysis of all cluster models have been carried out using the B3LYP hybrid method at 6–31+G (d,p) basis set level for hydrogen, silicon, aluminum, oxygen, carbon, and sulfur atoms. The structures and energy changes of different coordination forms between methanethiol and H 3Si(OH)Al(OH) 2OSiH 3, dimethyl sulfide and H 3Si(OH)Al(OH) 2OSiH 3, methanethiol and H 3SiOSi(OH) 2OSiH 3, dimethyl sulfide and H 3SiOSi(OH) 2OSiH 3 complexes have been comparatively studied. The calculated results showed the nature of interactions that led to the formation of all complexes was van der Waals force confirmed by an insignificant change of geometric structures and properties. The conclusions that methanethiol and dimethyl sulfide molecules were adsorbed on bridging hydroxyl group prior to silanol group were obtained on the basis of adsorption heat, the most stable adsorption models of a 6 ring structure for interaction between bridging hydroxyl and methanethiol, and a 7 ring structure for interaction between bridging hydroxyl and dimethyl sulfide.