Iron(II) sulfate oxidation with oxygen on a Pt/C catalyst: A kinetic study

The kinetics of iron(II) sulfate oxidation with molecular oxygen on the 2% Pt/Sibunit catalyst was studied by a volumetric method at atmospheric pressure, T = 303 K, pH 0.33–2.4, FeSO₄] = 0.06?0.48 mol/l, and Fe₂(SO₄)₃] = 0?0.36 mol/l in the absence of diffusion limitations. Relationships were established between the reaction rate and the concentrations of Fe²⁺, Fe³⁺, H⁺, and Cl^? ions in the reaction solution. The kinetic isotope effect caused by the replacement of H₂O with D₂O and of H⁺ with D⁺ was measured. The dependence of Fe²⁺ and Fe³⁺ adsorption on the catalyst pretreatment conditions was studied. A reaction scheme is suggested, which includes oxygen adsorption, the formation of a Fe(II) complex with surface oxygen, and the one-electron reduction of oxygen. The last step can proceed via two pathways, namely, electron transfer with H⁺ addition and hydrogen atom transfer from the coordination sphere of the iron(II) aqua complex. A kinetic equation providing a satisfactory fit to experimental data is set up. Numerical values are determined for the rate constants of the individual steps of the scheme suggested.