Review on Reduction and Partial Oxidation of Organics in Photocatalytic (Membrane) Reactors

Traditional processes for making chemicals are unsustainable in terms of resources and environmental impact. The present paper is a review of the most recent advances in the application of selective photocatalytic reactions to organic synthesis, which, in the last years, has attracted the interest of the scientific community addressing on development of environmentally benign synthetic processes. Indeed, selective photocatalysis is operated at ambient temperature and pressure, needs no complex equipments, does not use dangerous chemical reagents and solvents, does not release harmful wastes into the environment and can utilize solar light. Reactions discussed in this paper, as a green approach for valuable fine chemical synthesis, are: i) photocatalytic hydrogenation and/or transfer hydrogenation of ketones and nitrocompounds by using both UV and visible light; ii) photocatalytic hydrogenation and selective partial hydrogenation of unsaturated compounds; iii) selective partial oxidation of alkanes, alkenes, alcohols, aliphatic acids, benzene and other aromatic compounds by using both UV and visible light. Use of Photocatalytic Membrane Reactors (PMRs) in reductions (e. g. CO2 to fuels) and in selective partial oxidations (e. g. benzene to phenol) is reported, evidencing that opening up of a new avenue is expected in organic syntheses, thanks to the synergy of heterogeneous photocatalysis and membrane processes. Nevertheless, these studies are still at nascent stady and much work is needed before taking advantage of PMRs potentiality at industrial level in this interdisciplinary area.