Hydrogen effects in hexane reactions over Al2O3 supported Pt, Ir and Pt–Ir catalysts

Abstract

Hexane was tested under similar conditions on Al₂O₃ supported Pt, Ir and Pt–Ir catalysts. A conventional impregnation on commercial alumina and a sol–gel procedure involving the introduction of the Pt or Ir components at the commencement of gelification were applied for the preparation of monometallic catalysts. Pt–Ir samples were prepared by co-impregnation or using a bimetallic complex precursor, [Ir(NH₃)₅Cl][PtCl₄], produced in the pores of the support. Increasing H₂ pressure at both 603 and 663 K enhanced the overall activity and the very pronounced hydrogenolysis on Ir. Non-degradative products, including isomers, methylcyclopentane, benzene and hexenes, showed, as a rule, maximum rates as a function of p(H₂) on Ir also, in agreement with earlier and present reports concerning Pt. Both Pt and Ir catalysts on a sol–gel alumina were superior in non-degradative reactions to their conventional counterparts. The hydrogenolysis activity of both bimetallic catalysts was below the average for Pt and Ir, indicating Pt–Ir interactions. These were more pronounced with Pt–Ir prepared from a complex precursor, showing a higher activity in non-degradative reactions, more manifest at 663 K.