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Title: Heterogeneous catalysis in solution by silver metal
Author: Johnston, Ronald Robert
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1965
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In the past, interest in the reduction of aqueous silver ion has arisen largely because of the catalytic importance of silver in the process of photographic development. In literature studies in aqueous solution, the metal has been used in the form of colloidal dispersions. As a consequence, the nature of the slow step has not been elucidated because tie rates of mass transport of reactants to the catalyst surface or, in most cases, even the area of the surface could not be determined. These kinetic results have been critically reviewed in this thesis and reinterpreted in terms of a recently developed theory of catalysis of redox reactions by metals. To provide some necessary experimental data on diffusion coefficients and electrode kinetics, a study was made of the electrodeposition of silver from various aqueous solutions containing complexing anions which had been used in the earlier work. Small rotating silver disks were employed for this purpose. Several large rotating silver disks(12-48 cm2 area) were developed to provide measurable catalytic effects for complete chemical reactions and were shown to conform to the Levich theory by measurement of diffusion coefficients of silver ion in aqueous nitrate and perchlorate solutions. These disks were used to study reduction of aqueous silver ion by ferrous ion in both perchlorate and sulphate media. Although the rate was depressed in perchlorate due to the low activity of the catalyst surface, in sulrhate media the measured rates were in better agreement with the above mentioned theory. With the ferrous-silver ion reaction in aqueous solution, it was shown that the autocatalytic effect of the particulate silver product can be virtually eliminated by allowing the reaction to occur in a centrifuge. By this technique it might be feasible to measure the homogeneous rates of solution reactions involving an autocatalytic solid.
Supervisor: Barrer, R. M. ; Spiro, M. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available