Oxidation of chloride to chlorine by CeIV ions mediated by different RuIV and IrIV oxide-based catalysts

Abstract

A number of different, characterised, supported and unsupported oxides of RuIV and IrIV have been tested for activity as a chlorine catalyst in the oxidation of brine by CeIV ions. All the different materials tested gave yields of chlorine of >90% and first-order kinetics for the reduction of the CeIV ions. The samples prepared by the Adams method were the most active of the materials tested and are typified by high surface areas and appreciable activities per unit area. The kinetics of the catalysed reduction of CeIV ions by brine were studied in detail using an RuIV oxide prepared by the Adams method and supported on TiO2 and the results were rationalised in terms of an electrochemical model in which the rate-determining step is the diffusion-controlled reduction of CeIV ions. In support of this model the measured activation energies for the oxidation of brine by CeIV ions, catalysed by either a supported or unsupported Adams catalyst, were both close (18–21 kJ mol–1) to that expected for a diffusion-controlled reaction (ca. 15 kJ mol–1).