Olefin Metathesis over Supported Rhenium Oxide Catalysts

Abstract

Metathesis of isobutylene with 2-butene and disproportionation of propylene were studied over the supported rhenium oxide catalysts using both flow and pulse reactor techniques. By the metathesis of isobutylene with 2-butene over Re₂O₇-Al₂O₃₂ catalysts containing, various amount of rhenium oxide, a satisfactry amount of isoamylenes was obtained. The maximum activity was observed in the range from about 5% to 7% Re. The rate of isomerization between cis-2-butene and trans-2-butene is very fast and the mechanism of this reaction over these catalysts was assumed to be the same as that of metathesis.
With rising pretreatment temperature of the catalysts, more water is desorbed through two steps from the surface of the catalysts. At the first step of water desorption, the active site for the polymerization of propylene appears and at the second step which is accompanied by oxygen, the active center for polymerization disappears and that for the disproportionation appears. On the other hand the activity for disprotionation of propylene over a Re₂O₇-SiO₂catalyst is relatively high even at such a low pretreatment temperature as 150°C.
From the above results it was considered that the active center for the olefin metathesis exists in slightly reduced Re ion and the acid site on the carrier is not concerned with the reaction directly.