A STUDY OF THE COBALT SITES IN COBALT AND IRON MOLYBDATE CATALYSTS BY EMISSION MOSSBAUER-SPECTROSCOPY

Molybdates samples containing 74MBq (2mCi) of cobalt 57 have been studied by emission Mossbauer spectroscopy. Spectra of (CoMoO4)-Co-57 exhibited the three usual Fe2+ doublets corresponding to alpha and beta-ferrous phases, and two Fe3+ doublets accounting for about one third of the absorption area. The Co2+ sites of beta (CoMoO4)-Co-57 phase exhibit higher quadrupole splittings, i.e. are more dissymmetrical than Fe2+ sites of beta-FeMoO4 phase. Cobalt and iron molybdates (FexCo1-xMoO4)-Co-57 provided spectra where only one Fe3+ doublet appeared and occupied less than 7% of the spectral area. It is concluded that a part of cobalt was present in (CoMoO4)-Co-57 as Co3+.