Influence of oxidation-reduction treatment on activity of Re/gamma-Al2O3 catalyst diluted with gamma-alumina

Hydrogenation and hydrogenolysis of benzene was studied by a pulse method o n Re/gamma -Al2O3 catalysts (1.04 and 10.4 wt.% Re) diluted with gamma -alu mina (1:10) and subjected to the oxidation-reduction or to the direct reduc tion treatment. It was found that after direct reduction in hydrogen the ac tivity (per gram Re) of the undiluted and diluted catalysts was almost iden tical. 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/g amma -Al2O3 catalyst, but not for the diluted low-loaded catalyst. The resu lts can be explained in terms of redistribution of ReO4 groups over the alu mina surface. Oxidation of the diluted high-loaded catalyst caused migratio n of rhenium oxide to the admired support and after reduction in hydrogen t his led to the redispersion of metallic phase larger than the undiluted sam ple. The activity data agree well with the Hz chemisorption and TEM results . (C) 2001 Elsevier Science B.V. All rights reserved.