Mercaptan-Mediated Ethylene Formation in Sulfur Oxidative Ethane Dehydrogenation on Iron Sulfide (FeS<sub>2</sub>) Catalysts.

Abstract

Ethylene is a key feedstock for numerous industrial chemicals. It is conventionally produced via steam cracking, yet considerations of selectivity and downstream separation costs continue to motivate investigations of alternate production pathways. Catalytic ethane dehydrogenation (EDH) offers such an alternative, while the use of soft oxidants, such as sulfur, may alleviate the overoxidation that is characteristic of traditional oxidative approaches. This study explores the effectiveness of sulfur (S₂) as an alternative oxidant for EDH. Using periodic density functional theory calculations, we explore the surface structures and sulfur coverages of FeS₂ catalysts, which we have recently shown to be effective for this chemistry, under relevant temperature and pressure conditions. The results reveal that the catalyst experiences temperature-dependent surface sulfidation and that surface S-dimer species are catalytically active. The associated reaction energetics demonstrate that ethylene may be formed via both a mixed surface/gas phase mercaptan-mediated pathway and a conventional surface-catalyzed route on sulfur-covered FeS₂ facets at intermediate temperatures. The preferred pathways and associated activation barriers are sensitive to the local structure of surface facets, with the sulfur vacancy formation energy and the average valence p-state electronic energy of surface sulfur atoms identified as plausible descriptors for the catalytic activity. The aggregate results shed light on the mechanistic interplay of sulfur and ethane on FeS₂ surfaces and offer a potential pathway for developing efficient catalysts utilizing sulfur-based oxidants for selective ethylene production.