Structure sensitivity of benzene hydrogenation on supported Pt catalysts

Abstract

The activity of a series of supported Pt catalysts for the hydrogenation of benzene has been evaluated at 80 °C and 1 atm total pressure. Three sets of catalysts with a wide range of percent metal exposed were investigated: Pt/Al₂O₃, Pt/Al₂O₃-Cl and Pt/SiO₂, with the Cl series obtained by exposure of Pt/Al₂O₃ to HCl or CCl₄. The structure sensitivity of benzene hydrogenation on the chloride-free Pt/Al₂O₃ depended upon the reduction temperature employed in pretreatment. In general, the reaction was structure insensitive for high-temperature reduction (>450 °C), while for lower temperatures (100 and 300 °C) activity decreased with decreasing particle size. For Pt/Al₂O₃-Cl the reactivity behaviour was a function of chloride level. At low loadings (0.3 wt. %) the behaviour of these catalysts was similar to that of their chloride-free counterparts; however, a higher loading set (1 wt.%) showed a depression in activity over the entire particle size range except for very low percentage exposed metal. This is to be compared with the apparent augmentation of the activity of Pt/Al₂O₃ after HCl treatment reported by Bernard and Primet (J. Chem. Soc., Faraday Trans., 1990, 86, 567) for n-butane isomerization and that for methylcyclopropane hydrogenolysis (after either HCl or CCl₄) reported by Ollendorff et al.(Appl. Catal., 1990, 62, 85), since these reactions are sensitive to acidity in a fashion that is not possible with benzene.