Boghosian, S.

Chrissanthopoulos, A.

Fehrmann, Rasmus

Electronic absorption (UV/VIS) spectra have been obtained at 450 degrees C from V2O5-K2S2O7 molten mixtures in SO2 ( P-SO2 = 0 - 1.2 atm) gas atmospheres. The data are in agreement with the V-V reversible arrow V-IV equilibrium: (VO)(2)O(SO4)(4)(4-)(l) + SO2(g) - 2VO(SO4)(2)(2-)(l) + SO3(g). Sulfur dioxide does not coordinate to the V-V complex but starts significantly to coordinate to V-IV for P-SO2 &gt; 0 4 atm in accordance with the equilibrium: VO(SO4)(2)(2-)(l) + SO2(g) reversible arrow VO(SO4)(2)SO22-(l). Furthermore, high temperature Raman spectroscopy has been used to establish the structural and vibrational properties of the vanadium complexes formed in the molten salt-gas system V2O5-M2S2O7-M2SO4/SO2-O-2 (M = K or Cs). The spectral features and the exploitation of the relative Raman intensities indicate that the (VO)(2)O(SO4)(4)(+) dimeric complex unit which possesses a V-O-V bridge is formed in the V2O5-M2S2O7 molten mixtures. Interaction with SO2 or addition of sulfate leads to cleavage of the V-O-V bridge and formation of the (VO)-O-IV(SO4)(2)(2-) or (VO2)-O-V(SO4)(2)(3-) complex units respectively. The most prominent Raman bands due to the V-V and V-IV complexes formed are assigned and the spectral data are discussed in terms of possible structural models

Structural and Redox Properties of Vanadium Complexes in Molten Salts of Interest for the Catalytic Oxidation of Sulfur Dioxide

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