MnCl₂·4H₂O and Tiron (disodium 4,5-dihydroxy-1,3-benzenedisulfonate) rapidly remove dioxygen (O₂) from aqueous solution at a rate of ∼20 mg L⁻¹ min⁻¹ with turnover frequencies (TOFs) of up to 440 000 h⁻¹ in the pH range 7.50–11.0 and at 20–50 °C using hydroxylamine (NH₂OH) as reducing substrate. These solutions remain deoxygenated for several hours despite being open to the atmosphere. During this time there is a steady rise in the concentration of in situ generated hydrogen peroxide (H₂O₂), reaching ∼12 mM after 17 h. The order of selectivity for selected 1st row transition metals was found to be: Mn(II) ≫ Co(II)∼Cu(II)∼Fe(II). No deuterium isotope effect was observed, which suggests that an electron transfer is the rate determining step. A mechanism is proposed that involves two 1-electron transfers from bound NH₂OH to bound O₂ to produce H₂O₂ concomitant with two proton transfers from catecholate oxygen atoms. This system can act as an anti-corrosion formulation as the catalytic reduction of O₂ results in the removal of O₂ from open aqueous solutions and the in situ generated H₂O₂ can be used as a biocide e.g. to kill L. pneumophila. Batch experiments were carried out to confirm the feasibility of this system to simultaneously inhibit corrosion and also potentially disinfect central heating and cooling water systems.