Skeletal isomerization of hexenes on tungsten oxide supported on porous alpha-alumina

The isomerization of hexenes on tungsten oxide supported on a porous alpha- Al2O3 catalyst with a coverage approaching one monolayer has been studied. The support used is a porous monolith of alpha-alumina prepared by a novel method. It appears that this catalyst exhibits high and very stable activit y and isomerization selectivity under a hydrogen stream at 350 degrees C or at higher temperatures. No pretreatment is necessary to induce the activit y. The skeletal isomerization proceeds only through an acidic mechanism inc luding carbenium ion rearrangements. The catalyst was characterized by XPS, XANES, XRD, and TPR. The acidic character of the fresh calcined surface wa s attributed to the presence of amorphous tungsten oxide species in interac tion with the support, as Lewis acidic sites, and to the presence of OH gro ups as Bronsted acidic sites. Such a catalyst has less resistance to poison ing by carbonaceous residues at low temperature (200 degrees C), but is ful ly rejuvenated by a simple exposure to hydrogen at 350 degrees C. (C) 1999 Academic Press.