Electron paramagnetic resonance study of catalysts derived from molybdenum hexacarbonyl

Abstract

E.p.r. spectroscopy has been used to study supported molybdenum hexacarbonyl olefin dispproportionation catalysts. Activation of silica and alumina supported catalysts causes the appearance of a signal attributed to molybdenum(V) in square pyramidal co-ordination. Exposure of activated catalysts to oxygen gives a signal due to O^– ₂, probably formed by electron transfer from tetrahedrally co-ordinated molybdenum(V). A second strongly adsorbed O^– ₂ species obtained on alumina supported catalysts is associated with exposed aluminium ions in the support. The square pyramidal molybdenum(V) species cannot be correlated with the activity of the catalysts for propene disproportionation, and it is suggested that the active species is a precursor of the tetrahedral molybdenum(V), possibly molybdenum(IV).