(740e) High Selectivity of Modified ?-Al2O3 for Propane Dehydrogenation Under H2s Treatment and Co-Feed

Natural gas is often sour, containing varying amounts of H₂S. Moreover, the delayed release of H₂S in shale gas reserves has also been reported, which underlines the importance of developing a versatile sour-gas-tolerant catalyst for natural gas monetization. While sulfur for decades has been regarded as catalyst poison, we seek to attain the catalytic routes where H₂S could serve as a co-catalyst or a co-reactant. This study focuses on a novel route for propylene production using an alumina supported metal-sulfide catalyst for propane dehydrogenation with co-feeding H₂S. We report an unexpectedly high selectivity of γ-Al₂O₃ and Sn/Al₂O₃ catalysts for propane dehydrogenation upon pretreatment and co-feeding of H₂S. Specifically, we observe that selectivity of 94.2% (to propylene) and 16.4% propane conversion can be obtained at 560 °C for C₃H₈:H₂:H₂S ratio of 1.1:1:0.1 on γ-Al₂O₃. Furthermore, the selectivity is enhanced to 94-98% when 1.5-10%Sn is deposited on Al₂O₃ at similar operating conditions, although the activity decreases with Sn loading. In situ DRIFTS combined with TEM, Raman and XRD indicated that impregnation of tin leads two types of Sn species, Sn anchored on alumina (OH-μ₁-Al_IV and HO- μ₁-Al_VI) and SnS upon H₂S pretreatment_­. We postulate that the active sites are Lewis acid sites (or acid-base site pairs) largely located on alumina (e.g., Al-O site pairs on 110 facets), and that H₂S or SnS_x largely poison unselective basic sites which lead to significant improvement in the selectivity over bare γ-Al₂O₃. Additionally, coke analysis showed that loss of sulfur is responsible for catalyst deactivation. Considering that a significant portion of natural gas streams are sour and removal of sulfur impurities before downstream processing can be prohibitively expensive, this study shows the potential of alumina/metal-sulfide as relatively benign class of catalysts for alkane activation, especially in the context of sour natural gas upgrading.