Catalysis of electrochemical reactions homogeneous

Hammouche M, Lexa D, Momenteau M, Saveant JM (1991) Chemical catalysis of electrochemical reactions—homogeneous catalysis of the electrochemical reduction of carbon dioxide by iron(O) porphyrins—role of the addition of magnesium cations. J Am Chem Soc... 

FIGURE 4.2. Redox and chemical homogeneous catalysis of electrochemical reactions. 

Chapters 4 and 5 are devoted to molecular and biomolecular catalysis of electrochemical reactions. As discussed earlier, molecular electrochemistry deals with transforming molecules by electrochemical means. With molecular catalysis of electrochemical reactions, we address the converse aspect of molecular electrochemistry how to use molecules to produce better electrochemistry. It is first important to distinguish redox catalysis from chemical catalysis. In the first case, the catalytic effect stems from the three-dimensional dispersion of the mediator (catalyst), which merely shuttles the electrons between the electrode and the reactant. In chemical catalysis, there is a more intimate interaction between the active form of the catalyst and the reactant. The differences between the two types of catalysis are illustrated by examples of homogeneous systems in which not only the rapidity of the catalytic process, but also the selectivity problems, are discussed. 

C. P. Andrieux, J. M. Dumas-Bouchiat, and J. M. Saveant. Homogeneous redox catalysis of electrochemical reactions Part IV. Kinetic controls in the homogeneous process as characterized by stationary and quasi-stationary electrochemical techniques, J. Electroanal. Chem. 113, 1-18 (1980). 

If a chemical reaction is operated in a flow reactor under fixed external conditions (temperature, partial pressures, flow rate etc.), usually also a steady-state (i.e., time-independent) rate of reaction will result. Quite frequently, however, a different response may result The rate varies more or less periodically with time. Oscillatory kinetics have been reported for quite different types of reactions, such as with the famous Belousov-Zha-botinsky reaction in homogeneous solutions (/) or with a series of electrochemical reactions (2). In heterogeneous catalysis, phenomena of this type were observed for the first time about 20 years ago by Wicke and coworkers (3, 4) with the oxidation of carbon monoxide at supported platinum catalysts, and have since then been investigated quite extensively with various reactions and catalysts (5-7). Parallel to these experimental studies, a number of mathematical models were also developed these were intended to describe the kinetics of the underlying elementary processes and their solutions revealed indeed quite often oscillatory behavior. In view of the fact that these models usually consist of a set of coupled nonlinear differential equations, this result is, however, by no means surprising, as will become evident later, and in particular it cannot be considered as a proof for the assumed underlying reaction mechanism. 

The last section was devoted to a range of real-world applications treated with ab initio molecular dynamics simulations. Results of gas to liquid phase transition simulations, structural and dynamical properties of liquids such as common solvents as well as the emerging neoteric media of ionic liquids were presented. After a short discussion of chemical reactions concerning homogeneous catalysis, we presented an overview of electrochemical reactions and related processes. 

FIGURE 2.16. Homogeneous catalysis electrochemical reactions. Reaction scheme and typical cyclic voltammetric responses. The reversible wave pertains to the mediator alone. The dotted curve is the response of the substrate alone. The third voltammogram corresponds to the mediator after addition of the substrate. 

FIGURE 2.1 9. Homogeneous catalysis electrochemical reactions with the homogeneous electron transfer as a rate-limiting step. Variation of the current ratio ip/yfp with the kinetic parameter, A, far a series of values of the excess factor, y. From left to right, logy = 0, 0.3, 0.5, 1,1.5, 2. 

FIGURE 2.23. Two-step homogeneous catalysis catalysis electrochemical reactions according to Scheme 2.11a. = 100. a Dimensionless voltammograms as a function of the... 

Fig. 3 Cyclic voltammetric analysis of the kinetics of an homogeneous redox enzyme reaction using a reversible one-electron mediator as the cosubstrate, taking as example the catalysis of the electrochemical oxidation of j8-D-glucose by glucose oxidase (6.5 pM) with ferrocene methanol as the cosubstrate at pH = 7 (ionic strength 0.1 M, temperature ...

Tetrapyrrolic macrocycles, such as porphyrin, consisted of four pyrrole units bonded by different bridges, for example methene in the case of porphyrins and aza-methene in the case of phthalocyanines [1]. These ligands can complex metal ion transition and the synthesized metallocomplexes are extremely stable [2, 3]. While some metalloporphyrins constitute the redox center of naturally occurring proteins, like heme in hemoglobin, metallophthalocyanines are purely synthetic molecules. The (electro) chemical properties of MN4 complexes have been widely studied and have been particularly used for the catalysis of several electrochemical reactions in homogeneous solutions [4]. It was shown that the electrochemical properties of a... 

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