What is the catalyst in the following mechanism?
Br₂(aq) + H₂O₂(aq) → 2Br–(aq) + O₂(g) + 2H+(aq)
2Br–(aq) + H₂O₂(aq) + 2H+(aq) → Br₂(aq) + 2H₂O(l)