Vanadium (V) complexes in molten salts of interest for the catalytic oxidation of sulphur dioxide

High temperature Raman spectroscopy is used for the first time for establishing the structural and vibrational properties of V-V complexes in V2O5-Cs2S2O7 (0 less than or equal to X-V2O5(0) less than or equal to 0.24) and V2O5-Cs2S2O7-Cs2SO4 (0 less than or equal to X-V2O5(0) less than or equal to 0.25) molten salt mixtures at 450 degrees C under static equilibrium conditions. Based on Raman band intensity correlations and band assignments it is found that the V-V complex present in V2O5-Cs2S2O7 molten mixtures has a dimeric (VO)(2)O(SO4)(4)(4-) configuration containing a V-O-V bridge. Addition of Cs2SO4 in V2O5-Cs2S2O7 mixtures results in the reaction of the V-V dimer with sulfate ions and the spectral data obtained are accounted for by the following reaction scheme: (VO)(2)O(SO4)(4)(4-) + 2SO(4)(4-) --> 2VO(2)(SO4)(3)(2-) + S2O72-. The results are of value for the progress on the mechanistic understanding of the SO2 oxidation at the molecular level.