Kinetics of corrosion of ruthenium dioxide hydrate by bromate ions under acidic conditions

Abstract

The kinetics of oxidative dissolution of powdered ruthenium dioxide hydrate, RuO₂·xH₂O, by bromate ions under acidic conditions (0.5 mol dm^–3 H₂SO₄) are studied as a function of [BrO^–₃], [RuO₂·xH₂O] and temperature. In the overall reaction the BrO^–₃ ion acts as a six-electron oxidant and the RuO₂·xH₂O is oxidised to RuO₄. The dissolution kinetics, monitored spectrometrically through the appearance of RuO₄, obey the inverse cubic rate law, implying that the powder is monodispersed and that the rate of dissolution is proportional to the instantaneous surface area. For each kinetic run the data were analysed using the inverse cubic rate law and a rate constant, k_obs, was obtained. Plots of both 1/k_obsvs. 1/[BrO^–₃] and log(initial rate)vs. log[RuO₂·xH₂O] gave good straight lines. These results were interpreted in terms of a mechanism in which the rate-determining step was the reaction between a Ru^IV surface site and a BrO^–₃ ion adsorbed onto it. The overall activation energy for the corrosion reaction was determined to be 44 ± 5 kJ mol^–1.