Activation and chain-carrying CH2 species in terminal alkene metathesis on molybdena–titania catalysts

Abstract

The metathesis reaction of terminal alkenes other than isobutene took place on MoO_3–x/TiO₂, whereas that of isobutene proceeded in the presence of ethylene and following treatment of the catalyst with SnMe₄ at room temperature. These results infer that chain-carrying CH₂ species are generated to only a small extent by the adsorption of isobutene on MoO_3–x/TiO₂, although they are formed by the adsorption of alk-1-enes and SnMe₄. The metathesis-inactive material, fully oxidized MoO₃/TiO₂, was changed to a metathesis-active catalyst by treating it with SnMe₄. This suggests that MoO₃/TiO₂ has no ability to yield CH₂ species with terminal alkenes but that these species can be supplied with SnMe₄. An analysis by X-ray photolectron spectroscopy infers that SnMe₄ adsorbed on MoO₃/TiO₂ releases methyl groups concomitant with the oxidation of Sn.