Elucidating the underlying surface chemistry of Sn/Al2O3 catalysts during the propane dehydrogenation in the presence of H2S co-feed

Abstract Incipient wetness impregnation was used to deposit dispersed tin (Sn) atoms on γ-Al2O3. The morphology and structure of the catalysts were characterized using Raman, X-ray Photoelectron Spectroscopy, and low energy ion scattering combined with N2-physisorption and in situ infrared diffuse reflectance spectroscopy (DRIFTS) using NH3 and CO2 as probe molecules, H2- temperature-programmed reduction (TPR), and steady-state reaction kinetics measurements. The effects of H2S on the surface chemical composition and structure of the resulting catalysts were systematically studied. The results showed isolated and well-dispersed Sn oxide sites of the deposited catalyst with nanoparticles observed only at relatively high coverages of 10% Sn at a coverage ranging from 0.48 to 2.8 Sn atoms nm-2. DRIFT spectroscopy evidenced a decrease in the number of Lewis acid sites on H2S treated Sn/Al2O3 suggesting surface tin species re-dispersing and blocking the acid sites of γ-Al2O3. Overall, the surface analysis results presented here suggest that the active catalytic sites in the presence of H2S involve Al2O3 rather than bulk sulfide and Sn atoms dispersed over alumina towards propane dehydrogenation.