Coordination chemical approach to catalytic oxidation reactions

Abstract

A model for describing oxidation catalysis is presented. The bonds between reactant and catalyst are considered to be similar to bonds in complexes, namely interactions between an electron pair donor (EPD) and an electron pair acceptor (EPA). Oxygen, which is a species of high electronegativity, is expected to adopt the role of an EPD, whose strength increases with the base strength of the catalyst. Thus, the activity of a catalyst should be associated with its base strength. There are, indeed, many results in the literature to support this idea. The tendency of a catalyst to deep (total) oxidation increases with its base strength, whereas for partial (selective) oxidation, catalysts of higher acid strength are more appropriate. To compensate the charge (of two electrons) transferred with O −2 to the reactant, a transfer of two electrons to the catalyst is assumed to take place, for which accessible EPA sites (metal cations) are indispensable. The mechanism for total oxidation is considered to be equal to that of partial oxidation, the essential difference being the EPD strength of the O −2 ions on the surface of the catalyst.