A large share of natural gas reserves is sour and can contain a significant amount of H 2 S. These streams are typically treated using energy-intensive separation methods to remove sour gas molecules to preserve downstream catalysts and equipment. In contrast, we investigate sour gas tolerant catalysts to devise catalytic processes for sour natural gas monetization without prior CO 2 and H 2 S removal.<br/>The catalytic dehydrogenation of propane (PDH) is the most direct and selective way to produce propylene and valorize propane from abundant natural and shale gas resources. Recent experimental and computation work has demonstrated that earth-abundant and environmentally benign bulk metal oxides, such as Al 2 O 3 , TiO 2, and ZrO 2, can exhibit good activity and selectivity for PDH. Recently, we showed that bulk γ-Al 2 O 3 catalyst shows high selectivity for propane dehydrogenation upon pretreatment and co-feeding with H 2 S. We report an unexpectedly high selectivity of γ-Al 2 O 3 catalysts for propane dehydrogenation upon pretreatment and co-feeding of H 2 S. Specifically, we observe that selectivity of 94% (to propylene) and 16% propane conversion can be obtained at 560 °C for C 3 H 8 :H 2 :H 2 S ratio of 1.1:1:0.1 on γ-Al 2 O 3 . Our results indicate that H 2 S can irreversibly modify the active sites of γ-Al 2 O 3 , 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 H 2 S. Subsequently, the selectivity can be further enhanced to 94-98% on modification of Al 2 O 3 via Sn modification at similar operating conditions. However, the initial activity decreases with Sn loading. In situ DRIFTS combined with AC-STEM, Raman, and XRD indicated that impregnation of tin leads to two types of Sn species, Sn anchored on alumina hydroxyl group and SnS upon H 2 S pretreatment. We postulate that the active sites are largely located on alumina (e.g., Al-O site pairs on 110 facets). Lastly, we<br/>have evaluated a spectrum of transition metal supported on alumina. We have determined that highly dispersed Fe species over γ-Al 2 O 3 can perform selective dehydrogenation in H 2 S at high conversion.

High selectivity of modified alumina for propane dehydrogenation under H2S treatment and co-feed

ACS Fall 2021

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