Characterization and Reactivity of Molecular Oxygen Species on Oxide Surfaces

The surface oxygen species can conveniently be divided into two broad classes, i.e., mononuclear and molecular. Molecular oxygen species are also formed on the surface. The characterization of the adsorbed species has improved markedly as isotopic labeling with 17O has become more widely used. Some novel forms of molecular oxygen species have been reported and, in particular, the reactivities of species have been studied. Molecular oxygen species have been also identified as intermediates in some biological reactions and are important as oxygen adducts in natural and artificial oxygen carriers. The chapter focuses on adsorbed molecular oxygen species, and shows how recent developments point the way toward an understanding of the role that they and the mononuclear forms of oxygen may play in oxidation reactions. There is a need for a holistic approach to the reaction mechanism which combines both a study of the intermediates by a variety of techniques coupled with an overall analysis of the reaction pathway. It is difficult to combine a general semiempirical approach with specialized characterization but such a synthesis is most likely to lead one to a better understanding of the complex surface phenomena.