Kinetics of propane dehydrogenation over Pt–Sn/Al2O3

Abstract

The kinetics of the gas-phase dehydrogenation of propane over Pt–Sn (1 : 1 mol ratio) supported on Al₂O₃ was investigated for the first time over the high range of reactant/products partial pressures (up to 0.875 atm). The Pt precursor was reduced to metallic form after a temperature-programmed reduction (TPR) at 873 K. X-ray photoelectron spectroscopy (XPS) analysis suggests that a Pt–Sn surface alloy forms, decreasing the H₂ adsorption on the Pt–Sn sites (5.6 nm in average size) relative to monometallic Pt (6.8 nm). We performed kinetic studies in the absence of mass/heat transfer limitations. The incorporation of Sn into Pt in Pt–Sn/Al₂O₃ enhanced the catalytic activity and stability when compared to Pt/Al₂O₃. We attribute this response to the surface electronic interaction between Pt and Sn. The initial propane consumption rate increases with the partial pressure of propane and decreases with the partial pressure of propene, while varying that of hydrogen has a negligible effect. Applying the Langmuir–Hinshelwood–Hougen–Watson (LHHW) approach, the most likely kinetic model is non-dissociative adsorption of propane with simultaneous release of H₂, where surface reaction is the rate-limiting step. Our results of the kinetic aspects provide practical insights relevant to propane dehydrogenation.