CO2 Reduction Using Molecular Photocatalysts

Carbon dioxide (CO2) as feedstock for fuels and chemicals in an era of depleting fossil fuels poses a challenging task for future generations. Solar light as ubiquitous source of energy can be applied for the photochemical reduction of CO2 with visible light active redox photosensitizers. For the reduction of CO2 with molecular catalysts, late-transition-metal complexes, such as fac-Re(bpy)(CO)3Cl, have first been applied in the 1980s to generate carbon monoxide (CO). Different metal catalysts have been identified over the years, allowing selective formation of either CO or formic acid (HCOOH), valuable chemicals and fuel precursors. In this chapter, various molecular photocatalytic systems consisting of redox photosensitizers (PS) and various CO2-reduction catalysts (CAT) are introduced and their mechanistic highlights are summarized. The second part of the chapter lays the foundation for the construction of supramolecular photocatalysts in which the photosensitizer and catalyst units are chemically connected. In the third part, hybrid catalysts are introduced for Z-scheme applications consisting of semiconductors and the previously described supramolecular photocatalysts for CO2 reduction.