A study of the cobalt sites in cobalt and iron molybdate catalysts by emission Mössbauer spectroscopy

Molybdates samples containing 74MBq (2mCi) of cobalt 57 have been studied by emission Mössbauer spectroscopy. Spectra of⁵⁷CoMoO₄ exhibited the three usual Fe²⁺ doublets corresponding to α and β ferrous phases, and two Fe³⁺ doublets accounting for about one third of the absorption area. The Co²⁺ sites of β⁵⁷CoMoO₄ phase exhibit higher quadrupole splittings, i.e. are more dissymmetrical than Fe²⁺ sites of βFeMoO₄ phase. Cobalt and iron molybdates Fe_x ⁵⁷Co_1?xMoO₄ 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 in⁵⁷CoMoO₄ as Co³⁺.