Molecular mechanism of heterogeneous oxidation — organic and solid state chemists' views

Abstract

Publisher Summary This chapter discusses the role of electrophilic oxygen that has been illustrated and the molecular mechanisms of C–H bond activation. The process of oxidation of a hydrocarbon molecule must begin with the activation of the C–H bond. In the processes of heterogeneous catalytic oxidation, heterolytic C–H bond cleavage on the acid–base pair of sites is usually considered. It has been concluded that in the activation of a C–H bond, at the surface of a transition metal oxide, with semiconducting properties, both parts of the cleaved C–H bond become attached to the surface oxide ions. The importance of the transfer of electrons, between the oxide and the hydrocarbon, and oxygen gas mixture, as a redox system, has been also illustrated in the chapter. In the course of desorption of the oxygenated hydrocarbon molecule, as a product of the reaction, an oxygen atom becomes extracted from the surface of the oxide catalyst, leaving behind an oxygen vacancy. Simultaneously, hydrogen atoms abstracted from the hydrocarbon molecules and present at the surface in the form of hydroxyl groups must be removed by dehydroxylation that also generates surface oxygen vacancies. The chapter also discusses about the transition metal oxide monolayer catalysts. Transition metal oxides are nonstoichiometric compounds, their composition depending on the equilibrium between the lattice and its constituents in the gas phase. Question has been raised, concerning the mechanism, by which the support influences the behavior of the monolayer. Introduction of clusters of transition metal oxides into the zeolite framework has also been discussed in the chapter. Such catalysts are now a subject of considerable interest.