Heterogeneous redox catalysis

The practical importance of heterogeneous redox catalysis to many industrial processes has been well-documented over the past decade. Although there has been much technological progress in fields such as mineralogy, electrodeless plating, chlor-alkali production, photographic development, hydrometallurgy and many artificial solar to chemical energy conversion systems, the fundamental processes involved are not always fully understood. There is a need, therefore, to investigate these processes further. Chapter 3 investigates the abilities of different carbon black materials to act as catalysts for the oxidation of brine to chlorine by ceric ions. The kinetics are studied as a function of various experimental parameters, a reaction mechanism is proposed and these results are readily interpreted using an electrochemical model. Chapter 4 follows on from Chapter 3 by extending the investigation to include a study of all the three forms of crystalline carbon (graphite, diamond and C₆₀) as chlorine catalysts. This chapter reports the first example of C₆₀ acting as a redox catalyst. Chapter 5 reports the kinetics and mechanism of a rare example of reversible heterogeneous redox catalysis, in which the oxidation of ruthenium (II) tris (2,2'-bipyridine) ions by thallic ions in nitric acid is catalysed by a dispersion of ruthenium dioxide hydrate. The reaction kinetics fit an electrochemical model of reversible heterogeneous redox catalysis, assuming the kinetics are diffusion-controlled. Chapter 6 similarly investigates the use of a variety of platinum powder dispersions to act as catalysts for the reaction studied in Chapter 5. It also includes a study to show that inert metal oxides can be used as antiflocculants to enhance the rate of heterogeneous catalysis by platinum group metals of this reaction, as well as irreversible redox reactions, such as water and brine oxidation. Chapter 7 describes a novel route for the removal of harmful bromate ions from drinking water. The reaction kinetics are studied both in water and in the presence of organic pollutants and an electrochemical model, in which the two participating redox couples are both electrochemically irreversible, is used to interpret the observed kinetics.