ISOMERIZATION OF N-HEXANE OVER CHLORINATED PT GAMMA-AL2O3 CATALYSTS/

Chlorided 0.57 wt. % Pt/gamma-Al2O3 is a moderately active and highly selective catalyst for the isomerization of n-hexane at 300 degrees C when an excess of H-2 is present. Chlorine, which is continuously lost from the catalyst, may be replaced by adding a small amount of chloro form to the reactant stream. The catalyst exhibits activity and high i somerization selectivity even at 150 degrees C. Under the conditions o f these lower temperature experiments, the equilibrium concentration o f C-6 alkenes would be only 8 x 10(-7) Torr. This suggests that the cl assical mechanism, which involves the formation of n-hexene on the Pt, is not applicable. Rather, it is proposed that isomerization of the a lkane occurs at acid sites on the catalyst, and the role of Pt is to c atalyze the hydrogenation of any alkenes that might be formed as a res ult of cracking reactions. At temperatures less than or equal to 300 d egrees C Bronsted acid sites are present in the catalyst, and presumab ly are responsible for the isomerization and cracking activity, but at higher temperatures Lewis acid sites play a dominant role.