why is sulphur dioxide an oxidizing agent?

In most cases, sulphur dioxide acts as a reducing agent with the half equation:
SO2 + 2H2O → SO42- + 4H+ + 2e-
For example, consider the redox reaction between SO2 and Br2:
SO2 + 2H2O + Br2 → SO42- + 4H+ + 2Br-
SO2 acts as a reducing agent which is oxidized (the oxidation number of S increases from +4 in SO2 to +6 in SO42-). Br2 acts as an oxidizing agent which is reduced (the oxidation number of Br decreases from 0 in Br2 to -1 in Br-).

I remember that there are only two cases that sulphur dioxide acts as an oxidizing agent.
(1) When burning Mg in SO2, SO2 acts as an oxidizing agent which oxidizes the Mg to MgO (the oxidation number of Mg increase from 0 in Mg to +2 in MgO), and the SO­2 is reduced to S (the oxidation number of S decreases from +4 in SO2 to 0 in S).
2Mg + SO2 → 2MgO + S
(2) In the reaction between H2S and SO2 at room temperature, SO2 acts as an oxidizing agent which oxidizes the H2S to S (the oxidation number of S increases from -2 in H2S to 0 in S), and the SO2 is reduced to S (the oxidation number of S decreases from +4 in SO2 to 0 in S).
2H2S + SO2 → 2H2O + 3S

what catalyst is used to oxidize sulphur dioxide to sulphite