Composition of V₂0₅-K₂SO₄ Catalysts during the Oxidation of Sulphur Dioxidet

Abstract

The composition of V205-K2SO₄ catalysts during the oxidation of sulphur dioxide, especially in its lower concentrations (0.2%), wa sstudied by means of TGA, DTA, X-ray diffractometry and chemical analysis in order to get further informations on the mechanism of the reaction. It was found that it took more than several hours for the catalyst to reach the equilibrium composition in the reacting gas (Fig.3, 6). This was considered to be one of the several reasons that the oxidation of sulphur dioxide generally required a longer time to reach the steady state. The effects of temperature on the absorbed volume of SO, by the catalyst and on the V5+/(V5 +V4+) ratio were studied in the range between 320 through 520°C. Absorbed SO, volume and V5+/(V5 d-V4+) ratio changed greatly at the temperature range of 400∼450°C(Fig.4, 7), and these changes could be correlated with the change in the reaction mechanism which occurred at the above mentioned temperature range. The catalytic activity, the absorbed volume of SOS, and the V51/(V5H-V4+) ratio of the catalyst at working state were plotted against catalyst composition in temperature less than 450T. These plots had inflection points in the vicinity of K2SO₄/V205=1 (Fig.11, 12, 13). This fact suggests that a catalytic active substance may exist in an equal molecular ratio of K2SO₄ and V205, and that the mechanism of the oxidation of sulphur dioxide will be more complicated than the ever proposed theory that K2S₂0, and VOSO₄ were produced from K2SO₄ and V205.