Catalyst Regeneration in SO₂ Oxidation

Steps:

• In atmospheric oxidation, NO₂ oxidizes SO₂ to SO₃, producing NO: SO₂ + NO₂ → SO₃ + NO.
• NO acts as an intermediate form of the catalyst.
• Atmospheric oxygen reoxidizes NO to NO₂, regenerating the active catalyst.
• The reaction NO + ½O₂ → NO₂ shows this reformation step.

Why D is correct:

• It depicts the oxidation of NO to NO₂, completing the catalytic cycle as per the mechanism where nitrogen oxides shuttle between oxidation states.

Why the others are wrong:

• A: Shows unrelated N₂O₄ formation from elemental nitrogen, not catalyst regeneration.
• B: Represents ammonia combustion to N₂, irrelevant to nitrogen oxide catalysis.
• C: Involves ammonium ion oxidation, using incorrect species for atmospheric NO/NO₂ cycle.

Final answer: D