Influence of the Severity of Reaction Conditions on the Promotional Effects of Tin in Pt–Sn/γ-Al2O3 Catalysts in Propane Dehydrogenation

The influence of the severity of reaction conditions on the promotional effects of tin in bimetallic Pt–Sn/γ-Al₂O₃ catalysts in the propane dehydrogenation was studied over a wide range of reaction conditions (550–600°C, H₂/C₃H₈ = 0.4–1.5 mol/mol). The catalysts containing 0.5 wt % Pt with variable (0–1.0 wt %) Sn loading were prepared by sequential impregnation and characterized by N₂-physisorption, TPR, TPD, EDX, and TEM techniques. When 0.25 wt % tin was added to the Pt/γ-Al₂O₃ catalyst, at H₂/C₃H₈ molar ratios of 0.8 and 1.5 and all temperatures, a sharp (up to 100%) increase in the propylene selectivity was observed. The propylene yield vs. Sn loading curves showed maxima near the Sn/Pt weight ratio of 1 independently of operating conditions. Upon addition of the optimum amount of Sn, the first-order decay rate constant decreased from 0.15 to 0.066 h^–1 at 550°C and H₂/C₃H₈ = 0.4, which roughly corresponded to doubling of the catalyst lifetime under this condition. The promoting effect of Sn on the catalyst performance was more pronounced under more severe reaction conditions required for higher propane conversions, i.e., at higher temperatures and lower H₂/C₃H₈ ratios in the feed.