Catalyst Regeneration in Atmospheric SO₂ Oxidation

Steps:

• NO₂ oxidizes SO₂ to SO₃, reducing NO₂ to NO and consuming the catalyst.
• Atmospheric oxygen reoxidizes NO back to NO₂ to sustain the cycle.
• Examine reactions for NO to NO₂ conversion.
• Option D matches this regeneration step.

Why D is correct:

• It shows NO oxidized to NO₂ by O₂, reforming the active catalyst in the NO/NO₂ cycle as defined by homogeneous catalysis principles.

Why the others are wrong:

• A: Forms NO₂ from N₂, initiating new catalyst rather than regenerating existing NO.
• B: Reduces NH₄⁺ to N₂, unrelated to nitrogen oxide catalysis.
• C: Oxidizes NH₃ to NO, producing catalyst precursor but not reforming it.

Final answer: D