Atomically dispersed tin-modified γ-alumina for selective propane dehydrogenation under H₂S co-feed

Developing an earth-abundant catalyst that is sulfur-tolerant, active, and highly selective is of great interest for valorizing natural gas streams containing sour gas. A tin-modified alumina catalyst is reported that is stable and selective for propane dehydrogenation in the presence of percent quantities of H₂S in the feed. In particular, Sn/Al₂O₃-S catalysts with 1.5-5% Sn content exhibit 98% selectivity with up to 16% conversion at 560 °C during the fourth cycle. Experimental and computational characterization shows that the active sites are the defect tricoordinated Al atoms. H₂S pretreatment further modifies a portion of these sites via exchanging a neighboring oxygen atom with sulfur, thereby rendering them more active and selective. At low loadings, Sn is atomically dispersed and selectively binds to hydroxyl groups or oxygen atoms on Al₂O₃. This prevents the formation of original (unmodified) defect sites on Al₂O₃ and improves overall selectivity. The activity and selectivity of the catalyst are heavily dependent on the chemical potential of sulfur and hydrogen because they influence both the relative concentration of the two types of sites and the overall reaction mechanism. Finally, the catalyst can be regenerated fully under a pure H₂S stream, thereby precluding treatment under oxygen, which can lead to sintering.