Characterization and catalytic performance of PtSn catalysts supported on Al2O3 and Na-doped Al2O3 in n-butane dehydrogenation

Abstract

PtSn/Al2O3 and PtSn/Al2O3-Na catalysts display important modifications of the metallic phase with respect to Pt/Al2O3 one. In this sense, TPR and XPS results show the presence of strong interactions between Pt and Sn, with probable alloy formation, which would be responsible for the decrease of the reaction rate and the increase of the activation energy in cyclohexane dehydrogenation. Besides the experiments of cyclopentane hydrogenolysis show that the alkali metal addition to bimetallic PtSn/Al2O3 catalysts completely eliminates the hydrogenolytic ensembles, which could be due to a geometric modification of the metallic phase. These important modifications in the nature of the metallic function due to the simultaneous addition of Na and Sn to Pt/Al2O3 are responsible for the excellent catalytic performance in the n-butane dehydrogenation, thus giving high conversions, selectivities to butenes higher than 95%, and lower deactivation capacity than those corresponding to bimetallic PtSn catalysts (with different Sn contents) supported on undoped alumina. The excellent stability of PtSn/Al 2O3-Na catalysts would be due to a low carbon formation during the reaction, such as it was observed from pulse experiments.