A number of different carbon blacks are tested for activity as chlorine catalysts in the oxidation of chloride (2 mol dm-" in 0.5 mol dme3 H$O,,) to chlorine by Ce'" ions, that is, 2Ce," + 2c,_ carb""b'ack -2Ce"' t Cl,. CC3lyit
All the carbon blacks tested gave high yields of chlorine (>80%), and the kinetics for the reduction of the CeIV ions were first order with respect to [Celv] and [catalyst]. An extra conductive black, ECB, was the most active of the carbon blacks tested and had the highest BET surface area (1000 m* g-l). The results of a detailed kinetic study of the above reaction, mediated by ECB, are rationalised in terms of an electrochemical modei in which the Nemstian reduction of CelV ions is coupled to the irreversible (electrochemical) oxidation of chloride to chtorine, via the micro-electrode particles of the carbon black, with at least a monolayer covering of Ce"' sulphate. In support of this model, the activation energy for the oxidation of brine on the surface of ECB, derived from kinetic data using the model, was found to be 30 kJ mol-', which compares favourabiy to that observed by others for the oxidation of brine on macro-electrodes of graphite.