Influence of iridium content on the behavior of Pt-Ir/Al2O3 and Pt-Ir/TiO2 catalysts for selective ring opening of naphthenes

The influence of Ir content on the properties of Pt-Ir/Al2O3 and Pt-Ir/TiO2 catalysts for selective ring opening of naphthenes was studied. It was found that these catalysts display a strong Pt-Ir interaction but only a weak metal-support interaction. Catalyst acidities depend on the metal loading, but opposite effects were observed on alumina (decrease) or titania (increase) as the metal loading increased. The results obtained from test reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis) showed that titania supported catalysts were less active than their alumina supported counterparts. This behavior could be due to the partial blockage of metallic sites by migrated TiOx species and the sinterization of metallic phase during the reduction step. The methylcyclopentane ring opening reaction was found to occur through a partially selective mechanism, and an increase in activity as the Ir loading increased was observed. The selective mechanism was favored by higher total metal loadings, possibly due to an increase in the size of metallic aggregates. Alumina supported catalysts present higher ring opening selectivities. The activity for decalin ring opening increased both with metal loading and reaction temperature level. (C) 2012 Elsevier B.V. All rights reserved.