Interparticle hydrogen migration on PdAl 2O 3 catalysts for benzene hydrogenation?

Abstract

Hydrogenation and hydrogenolysis of benzene was studied by a pulse method on Re/γ-Al2O3 catalysts (1.04 and 10.4 wt.% Re) diluted with γ-alumina (1:10) and subjected to the oxidation–reduction or to the direct reduction treatment. It was found that after direct reduction in hydrogen the activity (per gram Re) of the undiluted and diluted catalysts was almost identical. The oxidation–reduction treatment of the undiluted catalysts caused increase in their activity for both reactions relative to that shown after direct reduction. Additional activity gain was found for diluted 10.4% Re/γ-Al2O3 catalyst, but not for the diluted low-loaded catalyst. The results can be explained in terms of redistribution of ReO4 groups over the alumina surface. Oxidation of the diluted high-loaded catalyst caused migration of rhenium oxide to the admixed support and after reduction in hydrogen this led to the redispersion of metallic phase larger than the undiluted sample. The activity data agree well with the H2 chemisorption and TEM results.