(694d) DFT Investigation of the Mechanism and Site Requirements for Alkane Dehydrogenation on Transition Metal Sulfide Catalysts

Olefins can be obtained from direct dehydrogenation of alkanes in shale gas. Conventional alkane direct dehydrogenation catalysts are either expensive or toxic [1]. Recent reports suggest that transition metal sulfides are promising alternatives because they have a high mass activity [2]. However, these catalysts deactivate rapidly due to sulfur loss. To elucidate the origin of the intrinsic activity and deactivation of these catalysts, we explored the mechanism and plausible active sites for dehydrogenation of ethane on the most commonly used transition metal sulfide, viz. molybdenum sulfide (MoS₂), using density functional theory. Specifically, the two catalytically active regions [3], Mo-edge and the S-edge of MoS₂ were considered in this study. Several possible sites on the two edges of MoS₂ were evaluated, including the coordinative unsaturated sites (CUS), sulfhydryl group, brim site, and the under coordinated Mo-S pair. Our results suggest the importance of sulfur atoms and coordinative unsaturation in direct C-H scission of ethane, the preference for desorption of adsorbed C₂H₄* relative to over-dehydrogenation, and the kinetic unfavourability of C-C scission relative to dehydrogenation.

The details of our calculations and models, the likely reaction mechanism, and supporting experimental evidence will be presented and discussed.

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