H₂ reduction behaviors and catalytic performance of bimetallic tin-modified platinum catalysts for propane dehydrogenation

Bimetallic Pt-Sn/MgAl₂O₄ catalysts with different metal concentrations, used for propane dehydrogenation, were prepared by the impregnation, coprecipitation-impregnation and sol-gel methods. Pore size distribution and surface acidity of the catalysts were studied by N₂ physisorption and temperature programmed desorption of ammonia (TPD-NH₃), respectively. Reduction behaviors of the catalysts were characterized by temperature programmed reduction (TPR) technique. In the catalysts containing 0.6 wt.% Sn, some platinum-modified by tin crystals were produced by association with acid sites of the support, where hydrogen reduction took place above 500°C. These tin-modified platinum species were found to be favorable for propane dehydrogenation reaction and also to be responsible for the improvement of the activity as tin content increases from 0.3 to 0.6 wt.%. Metal dispersion, pore size distribution and acidity of the support strongly impact the selectivity and stability of the catalysts. The sol-gel catalyst showed better selectivity but lower stability compared to other catalysts that can be explained by its very narrow pore size distribution and relatively stronger acidity as well as more homogeneous metal distribution on the support. When the catalysts were pretreated with oxygen and then hydrogen, their catalytic activities were significantly enhanced largely due to a better metal distribution on the support.