Compared selectivities of redox-catalyzed and direct electrochemical processes Part 1. Reactions in which product selection involves competition between dimerization and first-order reactions

In reactions where product selection involves competition between dimerization and first-order steps, selectivity may change on going from direct electrolysis to redox-catalyzed electrolysis. The variation of product distribution with pertinent competition parameters is rigorously and quantitatively established in each case. The physical reasons underlying this prediction are discussed. They are shown to derive from the development of spece-dependent concentration profile of the product selection intermediate. The particular form that this profile takes in each case is a function of the nature and rate of the step that produces the key intermediate and of the rates of the follow-up steps

Compared selectivities of redox-catalyzed and direct electrochemical processes Part 2. Reactions in which product selection involves competition between dimerization and deactivation followed by further reduction (or oxidation)

Possible changes in selectivity between redox-catalyzed processes and direct electrochemical reactions are discussed for a typical reaction scheme where product selection involves competition between a dimerization step and a reduction (or oxidation) pathway in which the reductant (or oxidant) is the catalyst on the one hand and the intermediate resulting from the first electron transfer on the other. This second reduction (or oxidation) pathway may or may not be controlled by the transformation of the first electron transfer intermediate into a second intermediate that undergoes a second electron transfer. In the former case, changes in selectivity between the two types of electrolysis conditions arise solely from the space dependence of the reactant and intermediate concentrations. They usaually favor the reduction (or oxidation) pathway in a redox-catalysed process rather than the direct reaction. In the converse situation, where the transformation of the first electron transfer intermediate is reversible and acts as a pre-equilibrium to the second electron transfer, one source of possible changes in selectivity also results from space depenence of the reactant and intermediate concentrations. However, it tends to play an opposite role, favoring the reduction (or oxidation) pathway in the direct reaction rather than the redox-catalyzed process. This effect is amplified if, as is usually the case, the catalyst is a weaker reductant (or oxidant) than the first electron transfer intermediate of the direct electrochemical reaction