Question

Indicate a chemical reaction involving a homogeneous catalyst.

Answer 1

A chemical reaction involving a homogeneous catalyst is the oxidation of sulfur dioxide (SO₂) to sulfur trioxide (SO₃) in the presence of nitric oxide (NO) as a catalyst, which occurs in the lead chamber process for the manufacture of sulfuric acid. In this reaction, the catalyst (NO) and the reactants (SO₂ and O₂) are in the same phase (gas phase), thus making this an example of homogeneous catalysis. The uncatalyzed oxidation of SO₂ to SO₃ is very slow. However, when nitric oxide is used as a catalyst, it reacts with oxygen to form an intermediate compound, nitrogen dioxide (NO₂), which then reacts with SO₂ to form SO₃ and regenerates the catalyst NO. This catalytic cycle provides an alternate pathway with lower activation energy, speeding up the reaction:

\[\ce{2 SO2_{(g)} + O2_{(g)} -> 2 SO3_{(g)}}\] (Uncatalyzed, very slow)

With NO catalyst:

\[\ce{2 NO_{(g)} + O2_{(g)} -> 2 NO2_{(g)}}\] (Intermediate formation)

\[\ce{2 NO2_{(g)} + 2 SO2_{(g)} -> 2 NO_{(g)} + 2 SO3_{(g)}}\] (Catalyst regeneration and product formation)

Thus, the presence of the homogeneous catalyst NO increases the rate of oxidation of SO₂ to SO₃ by providing an intermediate compound and an alternate reaction pathway with lower activation energy.