Hydrogenation of Aromatic Hydrocarbons over Supported Pt Catalysts .II. Toluene Hydrogenation

Abstract

Vapor-phase toluene hydrogenation was investigated over Pt supported on SiO 2, η-Al 2O 3, SiO 2 · Al 2O 3 and TiO 2. As with benzene, activation energies and reaction orders had no dependence on the support. The E A values were 12 ± 2 kcal/mol and the partial pressure dependence on toluene was near zero, i.e. essentially the same as for benzene; however, the H 2 pressure dependence increased from less than 0.7 at 333 K to over unity at 373 K. The turnover frequencies were four times higher with the most acidic support compared to the least acidic support, i.e., at 333 K under 50 Torr toluene and 685 Torr H 2, the TOF on 0.24% Pt/SiO 2 · Al 2O 3 was 0.112 s −1, whereas it was 0.027s −1 on 0.96% Pt/SiO 2. This rate enhancement is attributed to an additional hydrogenation reaction occurring via hydrogen spilling over onto the support and reacting with aromatic molecules adsorbed on acid sites on the oxide. Deactivation was less of a problem with toluene compared to benzene.