A theoretical investigation into the demethylation mechanism of dimethylsulfide over the W3O6 cluster

Abstract

Understanding how dimethyl sulfide (DMS) breaks down to form value-added products such as methanol on transition metal oxide catalysts is important for improving desulfurization processes. In this study, the reaction mechanism over a tungsten oxide cluster (W₃O₆) is elucidated using density functional theory (DFT) at the M06-L/LANL2DZ/aug-cc-pVTZ level of theory. Two competing mechanistic pathways were discovered over the W₃O₆ cluster: Pathway A) direct demethylation followed by methanol desorption and Pathway B) a water-assisted concerted demethylation pathway. Pathway A involves sequential steps with a moderate demethylation barrier (49.43 kcal/mol), but a significantly higher barrier (68.78 kcal/mol) for subsequent methanol formation, imposing a kinetic bottleneck. Remarkably, Pathway B, mediated by an explicit water molecule, facilitates a lower-barrier concerted transformation (56.19 kcal/mol), effectively bypassing the high-energy intermediate. Kinetic modeling via Transition State Theory and the Energetic Span Model reveal that despite the very low turnover frequency (TOF = 9.29 × 10−30 s⁻¹), the water-assisted pathway is energetically superior. These findings highlight the important role of water in helping the reaction proceed and offer insight for designing better catalysts for sulfur removal from DMS to methanol over the W₃O₆ cluster.