Structure of the Vanadium-Potassium Catalyst during the Oxidation of Sulfur Dioxide and the Oxidation Mechanism

The structure of vanadium-potassium catalyst in gas mixtures of various compositions of SO2, SO3, and O2was investigated at 500, 550, and 600°C to elucidate the mechanism of SO2 oxidation on the catalyst. It was found that in the catalyst 50–70% of V(IV) is in VO2+-form, and the rest of the vanadium forms large vanadium-oxygen networks. It was also found that both the reduction of V(V) with SO2 and oxidation of V(IV) with oxygen are in equilibrium and the desorption of SO3 from the molten catalyst into gas phase seems to be the rate-determining step in SO2 oxidation. On the basis of this mechanism, the reaction rate of SO2 oxidation can be formulated as follows, dSO3⁄dt=k′(SO3)=kPSO2·PO21⁄2. For the sake of confirmation, the kinetics of SO2 oxidation (below 10% conversion) over vanadium-potassium catalyst was measured by a flow method at 500, 550, and 600°C over gas compositions of SO2=5∼24% and O2=10∼36%. It was found that the rate expression was correct.