Heterogeneous Photocatalytic Systems for Partial and Selective Oxidation of Alcohols and Polyols

Photocatalysis is becoming particularly important in the realization of partial and selective oxidations of organic substrates, including alcohols and polyols, and at the same time is an example of green catalysis since it moves towards a “sustainable chemistry” with a minimal environmental impact. Heterogeneous systems with well-defined textural characteristics represent a suitable means to tailor the selectivity of photocatalytic processes. Here, we describe the most significant features of photocatalytic systems and the achievements in the partial oxidation of various classes of alcohols, with a focus on titanium dioxide, other semiconducting oxides and polyoxotungstates, soluble models of semiconducting oxides. These compounds share similar primary photoreactions: light absorption causes a charge separation with formation of positive vacancies able to initiate the oxidation of many organic substrates. Works here discussed concern photooxidation reactions carried out in the presence of O2, whose role in not only that of scavenging the photogenerated electrons but also that of producing active oxygen species that take part to the overall oxidation process. We emphasize that the combination of the advances in the preparation of nanostructured materials with mechanistic knowledge, derived from surface science and molecular level investigations, is actually the goal in order to achieve optimal tailoring of photoactive materials for obtaining high selectivity.