Mechanisms of Some Heterogeneous Photocatalytic Reactions of Oxidation Occurring via Oxygen Atom Transfer

Insights into the mechanisms of oxygen atom transfer in the photooxidation of organic compounds for heterogeneous photocatalytic systems have been presented. These reactions have a wide variety of practical applications in chemistry, biology, and applied sciences. The role of the oxygen atom transfer mechanism in homogeneous photocatalysis has been investigated for nearly a century. Relatively little attention has been paid to the disclosure of oxygen atom transfer reactions in heterogeneous photocatalytic systems. This chapter discusses some problems related to the catalytic oxygen atom transfer in the oxidation of organic compounds, mainly with dioxygen, under UV irradiation or visible light, in heterogeneous reaction systems. Various active oxygen species, including oxygen atom transfer agents, as reaction intermediates can be generated in these systems. Depending on the nature of the active oxygen species, including metal-oxo compounds, the photoassisted catalytic oxygen atom transfer can occur mainly by the primary photoexcitation of either the catalyst or its photosensitive solid support, in rare cases, also the catalyst/support complex. The peculiarities of the mechanism of photo-driven oxygen atom transfer were mainly exemplified by the reactions occurring in heterogeneous catalytic systems containing transition metal oxides, their metalorganic complexes, and other photosensitive solid materials, including heterogenized homogeneous photocatalysts on the different supports, such as the transition metal-oxo complexes on the semiconductor materials. Special attention has been paid to the chemistry of TiO2 and TiO2-based semiconductor photocatalysis from the point of view of the reaction mechanisms, including oxygen atom transfer reactions.

Keywords: Oxygen atom transfer, Heterogeneous photocatalytic reactions, Reaction mechanism