Elucidating the origin of selective dehydrogenation of propane on γ-alumina under H₂S treatment and co-feed

A bulk γ-Al₂O₃ catalyst shows high selectivity for propane dehydrogenation upon pretreatment and co-feeding with H₂S. The reaction kinetics, deactivation rates, and active sites for propane dehydrogenation on this catalyst were characterized using fixed bed conversion studies, NH₃-TPD, O₂-TPO, XPS, and density functional theory (DFT). Specifically, we observe that the selectivity to propylene was 94% at ca. 16% propane conversion at 560 °C for a C₃H₈:H₂:H₂S ratio of 1.1:1:0.1 on γ-Al₂O₃. Our results indicate that H₂S can irreversibly modify the active sites of γ-Al₂O₃, postulated to be defect sites on the 110 facet comprised of a tri-coordinated Al atom, such that the modified site was more active and selective towards propylene and less inhibited by co-fed H₂S. Along with XPS and O₂-TPO, the dehydrogenation-regeneration experiments suggest the formation of sulfurous coke and strong adsorption of reaction products result in a less active catalyst. This study shows the potential of alumina/metal-sulfide as an earth-abundant and relatively benign class of catalysts for alkane activation, especially in the context of sour natural gas upgrading.