Framework composition and activity of platinum-containing high-silica zeolites in n-hexane isomerization

The conversion of n-hexane on Pt-containing dealuminated mordenites and ZSM-5 zeolites was studied. The framework composition and the concentrations of extraframework aluminum compounds in mordenites were determined by X-ray diffraction analysis. It was demonstrated that the aluminum content of the framework affected the activity in n-hexane isomerization. It was found that a Pt-mordenite catalyst containing a considerable amount of extraframework aluminum compounds exhibited maximum activity. A quantum-chemical study of the interaction of platinum with Brønsted and Lewis acid sites was performed. It was hypothesized that oxidized surface platinum nanoparticles were the active sites of Pt-containing high-silica zeolites. These nanoparticles were formed by the interaction of platinum clusters with proton sites or extraframework aluminum compounds. An alternative mechanism was proposed for the conversion of alkanes to exclude the direct participation of acid sites.