Comparison of platinum-iridium bimetallic catalysts supported on γ-alumina and HY-zeolite in n-hexane reforming reaction

The characteristics and activity, selectivity and stability of Pt-Ir bimetallic catalysts supported on γ-Al₂O₃ and HY-zeolite were examined using hydrogen chemisorption on catalysts calcined at different temperatures as well as by catalyst performance for n-hexane reforming at 573-773 K and atmospheric pressure. All the catalysts used in this study were prepared by impregnation. The Pt-Ir/ HY and Pt-Ir/ Al₂O₃ calcined at 773 K did not exhibit severe oxidative agglomeration, in contrast to monometallic iridium catalysts, and their activity and selectivity in n-hexane reforming were quite different from those of monometallic platinum or iridium catalysts. The catalysts supported on HY-zeolite showed high activity for isomerization while γ-Al₂O₃-supported catalysts had high activity for dehydrocyclization. Deactivation with reaction time was much more pronounced on HY-zeolite-supported catalysts. Pt-Ir catalysts supported on Al₂O₃ and HY showed high selectivity and activity to high-octane value hydrocarbons when the both metals were present in equal amount, 0.5 wt.-%. Especially the HY-zeolite-supported Pt-Ir bimetallic catalyst showed a good performance for producing high-octane hydrocarbons containing less amounts of aromatic compounds. It may be concluded that the nature of the support greatly affected the catalytic properties of Pt-Ir bimetallic catalysts for n-hexane reforming.