OLEFIN METATHESIS ON SUPPORTED RHENIUM CATALYSTS ACTIVATED BY GAMMA-IRRADIATION

A new approach to the activation of Re2O7/Al2O3 and Re2O7/Al2O3 . SiO2 for low-temperature olefin metathesis has been developed. After heati ng in oxygen and then in vacuum at 873 K, the catalysts were subjected to gamma-irradiation from a Co-60 source in the presence of methane, butane, or carbon monoxide at ambient temperature. IR data revealed th at, upon gamma-irradiation, reduced Re species (metal ions in lower ox idation states and rhenium carbonyls) were produced. After evacuation at 293 or 423 K, catalytic activities of the gamma-irradiated samples for olefin metathesis at 293 K were measured. The turnover frequencies (TOF) in propene metathesis for the Re-catalysts irradiated in CH4 or C4H10 were found to be approximately one order of magnitude higher th an those for the unirradiated catalysts. The TOF for the catalysts irr adiated in CO significantly increased after treatment with cyclopropan e at 293 K. In the liquid-phase metathesis of hex-1-ene, turnover numb ers as high as 1100-2700 mol C-6/mol Re (selectivity 90-98%) were obta ined for the irradiated catalysts. It is suggested that gamma-irradiat ion in the presence of alkanes induces a series of chemical transforma tions of the supported metal ions and can produce surface metal-carben e complexes which are active intermediates in metathesis.