This disclosure relates to a method of managing a sulphur-containing species from a sour liquid, the method comprising: providing a sour liquid comprising sulphur-containing species; introducing a halogen-based catalyst to the sour liquid, the halogen-based catalyst being complexed with a second species; introducing an oxidant to the sour liquid; and reacting the sulphur-containing species, the halogen-based catalyst and the oxidant. The second species may be an ethoxylate or propoxylate species. The disclosure also relates to a composition comprising a sour liquid, a hydrogen-based catalyst complexed with a second species, and an oxidant, a use of a halogen-based catalyst that is complexed with a second species for the treatment of a sulphur-containing species in a sour liquid, and a composition containing a halogen-based catalyst that is complexed with a second species in a suitable carrier for use in the treatment of a sulphur-containing species in a sour liquid.