Metal assessment for the catalytic reduction of bromate in water under hydrogen

• Noble metals supported on activated carbon promote the reduction of bromate under H2.
• Palladium, platinum, ruthenium and rhodium are the most efficient catalysts.
• Bromate removal corresponds to complete conversion into bromide.
• Activity is related to the dissociative adsorption energy of hydrogen.
• The role of H2 is clarified and the catalytic mechanism is discussed.

The presence of bromate ion in water and wastewater is a known problem due to its carcinogenic potential, and other toxic effects on human health. The catalytic reduction under hydrogen is an attractive process for its removal by conversion into bromide ion.Different metals (Pd, Pt, Ir, Rh, Ru, Fe, Sn, Cu, Zu and Ni) supported on activated carbon were assessed for the catalytic reduction of bromate under hydrogen at room temperature and pressure. All these catalysts are active in the conversion of bromate into bromide. Ruthenium, palladium, platinum and rhodium were shown to be the most efficient metals. When the available metal surface for reaction was considered, platinum showed the best activity. The trend of activities was associated to (and discussed on the basis of) the dissociative chemisorption energy of hydrogen over the metals.A mechanism for the reduction of bromate was proposed, involving reactions in the liquid phase, on the surface of the activated carbon support, and on the surface of the supported metal particles. It is proposed that the reaction mechanism on the surface of the metal catalysts comprises the decomposition of hydrogen and subsequent reaction with bromate. This reaction leads to the release of bromide ion and water. The oxidized metal is then reduced by hydrogen, thus closing the catalytic cycle.