Metathesis of hexene-1 over supported rheniamolybdena-alumina catalysts

Abstract

The metathesis of hexene-1 was investigated on Re-, Mo- and Re-Mo-Al 2O 3 catalysts. Surface properties of the different catalysts were examined by chemisorption measurements and through the use of various physical methods. Isomerization of hexene-1 took place in parallel with metathesis, and the resulting internal olefins (hexene-2 and -3) participated actively in the total reaction of hexenes. Consequently, in addition to C 2 = and C 10 =, olefins ranging from C 3 = to C 9 = were obtained as products, which can be illustrated by the following overall reaction scheme : ▪ Catalyst characterization data from H 2 TPR, O 2 uptake, NH 3 TPD, XRD, ESR and ESCA measurements have indicated that all of the properties related to the surface state of the Mo oxide, such as the oxidation state and binding energies of Mo cations, the dispersion state, surface acidity etc., are scarcely influenced by the presence of Re cations. There is therefore no obvious interaction between the Re and Mo oxides on the surface. Based on the catalytic behaviour and surface properties of Re-Mo-Al 2O 3 observed in this work, a dual site mechanism was suggested in which the Re and Mo surface species exist independently. The main function of the Re species is to create more metathesis sites, which operate independently, while the isomerization reaction takes place on the acidic sites of the Mo-Al 2O 3 surface.