Isomerization of n-Hexane over Chlorinated Pt/γ-Al2O3 Catalysts

Article abstract of DOI:10.1002/jccs.199800073

Chlorided 0.57 wt. % Pt/γ-Al₂O₃ is a moderately active and highly selective catalyst for the isomerization of n-hexane at 300°C when an excess of H₂ is present. Chlorine, which is continuously lost from the catalyst, may be replaced by adding a small amount of chloroform to the reactant stream. The catalyst exhibits activity and high isomerization selectivity even at 150°C. Under the conditions of these lower temperature experiments, the equilibrium concentration of C₆ alkenes would be only 8 × 10^-7 Torr. This suggests that the classical mechanism, which involves the formation of n-hexene on the Pt, is not applicable. Rather, it is proposed that isomerization of the alkane occurs at acid sites on the catalyst, and the role of Pt is to catalyze the hydrogenation of any alkenes that might be formed as a result of cracking reactions. At temperatures ≤ 300°C Broensted acid sites are present in the catalyst, and presumably are responsible for the isomerization and cracking activity, but at higher temperatures Lewis acid sites play a dominant role.