Behavior of M₂SO₄-V₂0₅ and M₂SO₄-V₂0₄ Systems (M=Li, Na, K and Cs) in S0₃-S0₂-0₂ Atmosphere

Abstract

The chemical composition change of M2SO₄-V205 and M2SO₄-V204 systems (M=Li, Na, K and Cs) in various atmospheres of S02, air and S03-S02-02 mixtures derived from a 7% 50293% air mixture (about 90% conversion) was studied by means of differential thermal analysis, IR spectrometry, X-ray diffractometry and chemical analysis, and the relation between these behaviors and catalytic activities was discussed. The reduction of V205 by SO₂ (Fig.5 and 6) and the oxidation of V204 by air (Fig.7) were promoted by the M2SO₄ additives in the order (Cs)>(K)>(Na)>(Li). In V4+/Vtotai vs. M2SO₄/ V205 curves (Fig.14) obtained for M2SO₄-V205 systems in equilibrium with S03-S02-02 mixtures at 450°C, the maximum values of V4+/Vtotal were obtained in the range of M2504/ V20, =0.3-1.0 except Li2SO₄-V205 system. An amount of SO₃ absorbed in the M2SO₄ under the same condition, S03/M2SO₄ (mol ratio), was in the series (Cs)=4.02>1()=1.50>(Na)=0.86 >(Li)=0.20. When 2 M2SO₄-V205 (Fig.14) and 2 M2504-V204 systems (Fig.18) were in equilibrium with S03-S02-02 mixtures at 450°C respectively, the following V4+/Vtotal values were obtained for both systems; (Cs)=0.2, (K)=0.3-0.37, (Na)=0.4 and (Li)=1.0. From these results, it was estimated that M2SO₄ have the effect promoting the reduction of V20, and the oxidation of V204, and that SO₃ absorbed in M2SO₄ have the effect stabilizing the vanadium in the pentavalent state in the order (Cs)>(K)>(Na)>(Li). This order corresponded to the catalytic activity estimated from DTA studies in our previous paper. Li2SO₄ had no effect