| Popis: |
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 Bronsted 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. |
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