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Sulfur dioxide oxidation

المؤلف:  Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong

المصدر:  Shriver and Atkins Inorganic Chemistry ,5th E

الجزء والصفحة:  710

2025-10-19

590

Sulfur dioxide oxidation

Key point: The most widely used catalyst for the oxidation of SO₂ to SO₃ is molten potassium vanadate supported on a high-surface-area silica. The oxidation of SO₂ to SO₃ is a key step in the production of sulfuric acid (Section 16.13). The reaction of sulfur with oxygen to produce SO₃ gas is exergonic (∆_rG^O 371 kJ mol 1) but very slow, and the principal product of combustion is SO₂:

The combustion is followed by the catalytic oxidation of SO₂:

This step is also exothermic and thus, as with ammonia synthesis, has a less favourable equilibrium constant at elevated temperatures. The process is therefore generally run in stages. In the first stage, the combustion of sulfur raises the temperature to about 600ºC, but by cooling and pressurizing before the catalytic stage the equilibrium is driven to the right and high conversion of SO₂ to SO₃ is achieved. Several quite different catalytic systems have been used to catalyse the combination of SO₂ with O₂. The most widely used catalyst at present is potassium or caesium vanadate molten salt covering a high-surface-area silica. The current view of the mechanism of the re action is that the rate-determining step is the oxidation of V(IV) to V(V) by O₂ (Fig. 26.21). In the melt, the vanadium and oxide ions are part of a polyvanadate complex (Section 19.8), but little is known about the evolution of the oxo species.

Figure 26.21 Cycle showing the key elements involved in the oxidation of SO2 by V(V) compounds.