Catalyst Regeneration in SO₂ Oxidation

Steps:

• In atmospheric oxidation, NO₂ oxidizes SO₂ to SO₃, producing NO: SO₂ + NO₂ → SO₃ + NO.
• NO acts as the reduced form of the catalyst, which must be reoxidized to NO₂ for the cycle to continue.
• Regeneration occurs via reaction with atmospheric oxygen.
• Option D matches this: NO + 1/2 O₂ → NO₂, restoring NO₂.

Why D is correct:

• It depicts the oxidation step that recycles NO back to NO₂, per the catalytic cycle definition where the catalyst returns to its active form.

Why the others are wrong:

• A: Shows initial NO₂ formation from N₂, not catalyst recycling.
• B: Represents ammonia decomposition, unrelated to nitrogen oxide catalysis.
• C: Illustrates nitrate reduction in denitrification, not atmospheric SO₂ oxidation.

Final answer: D