The efficiency of photochemical systems for water cleavage into hydrogen and oxygen depends on the discovery of suitable catalysts for the reduction and oxidation reactions. The most widely studied oxygen catalytic material has been ruthenium dioxide hydrate; however, its activity depends on its degree of hydration. Highly hydrated ruthenium dioxide (RuO<SUB>2</SUB>.xH<SUB>2</SUB>O) is a poor O<SUB>2</SUB> catalyst and readily corrodes to RuO<SUB>4</SUB> in the presence of a strong oxidant. Few kinetic studies have been carried out on the dissolution of powder suspensions by various oxidants but RuO<SUB>2</SUB>.xH<SUB>2</SUB>O is an ideal subject for such a study since the corrosion reaction is relatively simple and can be followed spectrophotometrically. Chapter Three describes a model for the corrosion kinetics of a surface-controlled reaction for a powder dispersion whereby the particle size distribution follows the log-normal law. This was then tested on previously published kinetic data on the dissolution of a polydispersed powder suspension. In Chapter Four, a kinetic study of the dissolution of RuO<SUB>2</SUB>.xH<SUB>2</SUB>O by BrO<SUB>3<SUP>-</SUB></SUP> ions as a function of [BrO<SUB>3<SUP>-</SUB></SUP>], [RuO<SUB>2</SUB>.xH<SUB>2</SUB>O] and temperature is described. This showed that the kinetics obeyed the inverse cubic rate law, implying that the powder is monodispersed and the rate of dissolution is proportional to the surface area. The result of a kinetic study of the dissolution of RuO<SUB>2</SUB>.xH<SUB>2</SUB>O by Ce<SUP>IV</SUP> ions is described in Chapter Five. The kinetics were studied as a function of [Ce<SUP>IV</SUP>]:[RuO<SUB>2</SUB>.xH<SUB>2</SUB>O] ratio, [Ce<SUP>III</SUP>] and temperature. The results were interpreted using an electrochemical model in which the Ce<SUP>IV</SUP> reduction and the RuO<SUB>2</SUB>.xH<SUB>2</SUB>O oxidation are assumed to be highly reversible and irreversible processes respectively, mediated by the dissolving RuO<SUB>2</SUB>.xH<SUB>2</SUB>O microelectrode particles. Chapters Six and Seven describe the results of a kinetic study of water oxidation by Ce<SUP>IV</SUP> ions catalysed by Ru-Adams and RuO<SUB>2</SUB> (anhydrous), respectively. The kinetics were studied as a function of [Ce<SUP>III</SUP>], [catalyst] and temperature and were interpreted using an eletrochemical model of redox catalysis where the catalyst particles are considered as microelectrodes which mediate electron transfer between a Nernstian reaction (reduction of Ce<SUP>IV</SUP>) and an irreversible reaction (oxidation of water).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636367 |
| Date | January 1991 |
| Creators | Davies, H. L. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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