Polyoxometalates redox potential

Schwenz and Moore introduced cyclic voltammetry as a modem approach to electrochemistry experiments. Three new experiments exploit this technique. One uses the technique as a probe or electrode surface area (82). A second uses the method to study adsorption of polyoxometalates on graphite electrodes (83). A third studies the effect of micelles on the diffusion and redox potentials of the well-studied ferrocene system (84). 

From a mechanistic point of view it is important to realize that polyoxometalates may interact with peroxygen oxidants in several different ways depending on the composition, structure, and redox potential of the polyoxometalate compounds. On the one hand, one may expect reaction pathways typical for any oxotungstate or... 

Polyoxometalates (POMs) constitute a large family of anionic metal-oxygen clusters of early transition metals and have stimulated many current research activities in many fields of science such as catalysis, materials and medicine, because their chemical properties such as redox potentials, acidities and solubilities in various media can be finely tuned by choosing constituent elements and counter cations. In addition, POMs are thermally and oxidatively stable in comparison to organometal-lic complexes and enzymes. The use of POMs in oxidation catalysis has received much attention and has been reviewed several times. 

Various polyoxometalates can be reduced electrochemically and reversibly by several electrons at modest potentials (Section VILA), and these properties are exploited in photocatalysis and eiectrocatalysis. In both cases, redox properties of heteropolyanions (Fig. 49) and the organic reactants (Table XXXV) are the principal properties that control the catalytic performance. The selection of the electrode is also important in eiectrocatalysis. Photocatalysis by hereopoly-anions has been reported extensively, but there are only a few reports of eiectrocatalysis by these compounds. 

Since the application of POMs is so widespread across areas such as homogeneous and heterogeneous catalysis, as well as acid and redox catalysis, it is not possible to exhaustively review all the applications. Thus the rest of this chapter focuses only on the catalytic properties of the polyoxometallates in heterogeneous gas- or liquid-phase oxidation reactions, and reviews the most recent progress in the knowledge of their properties and working process, underlining both their potential and their limitations. 

Polyoxometalate anions have been studied for many years due to their wide range of interesting structural, redox, and catalytic properties [45]. The voltammetry of adhered polyoxometalate microparticles may provide an efficient method for obtaining their reversible potentials, even when product of reduction reacts with the ionic liquid itself or adventitious water [46-51]. 

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