Hydrogenolysis of n-hexane on Al2O3-supported Ir catalysts of various treatments

A high-dispersion 1 wt% Ir/Al2O3 with 1 wt% Cl as well as its counterparts with <0.2% Cl with or without sintering were tested in n-hexane reactions b etween 453 and 603 K. The Cl-containing catalyst was considerably less acti ve in this temperature range, unfavorable for bifunctional reactions. Hydro genolysis was the main reaction with selectivities up to 90%, along with mi nor amounts of nondegradative products. Single hydrogenolysis with some pre ference for splitting the molecule in the middle occurred at low temperatur es. That was replaced gradually by multiple rupture at higher temperatures. Increasing the hydrogen pressure at 513 K led to higher hydrogenolysis sel ectivities up to 98%; at the same time, it suppressed somewhat multiple fra gmentation. With less hydrogen present (at lower H-2 pressure or higher tem perature), a "soft" transition from single to multiple rupture occurred, Th e multiplicity of rupture was most pronounced on the larger crystallites of the sintered sample, whereas a terminal rupture seemed to appear on the Cl -free high-dispersion sample. Whenever single hydrogenolysis prevailed, the fragment distribution showed a slight preference to propane formation. (C) 1999 Academic Press.