Influence of oxidation-reduction treatment on activity and selectivity of Re supported on γ-alumina

The effect of oxidation-reduction treatment on the activity and selectivity of Re/gamma-Al2O3 catalysts (1.04 and 10.4 wt.% Re) for hydrogenation and hydrogenolysis of benzene was studied using a chromatographic pulse method. Treatment of the freshly reduced catalyst in an oxidizing atmosphere, at room temperature or at 673 K, increased its activity (per gram Re) for both the reactions with respect to that shown after direct reduction in hydrogen. The turnover frequencies (TOFs) for benzene hydrogenation were independent of the catalysts pretreatment, while the opposite was observed for benzene hydrogenolysis. Changes in selectivity were observed only for 1.04% Re/gamma-Al2O3 catalyst after oxidation at 673 K. The results are discussed in relation to the metal dispersion (or particle size) giving a better insight into the phenomenon of redispersion of supported rhenium. (C) 1998 Elsevier Science B.V. All rights reserved.