Photogeneration of Carbon Monoxide and of Hydrogen via Simultaneous Photochemical Reduction of Carbon Dioxide and Water by Visible-Light Irradiation of Organic Solutions Containing Tris(2,2'-bipyridine)ruthenium(II) and Cobalt(II) Species as Homogeneous Catalysts

Article abstract of DOI:10.1002/hlca.19860690514

CO and H2 are photogenerated simultaneously by visible-light irradiation of systems containing a photosensitizer, the ²⁺ complex, Co(II) species as homogeneous catalysts, which mediate CO2 and H2O reduction by intermediate formation of Co(I), a tertiary amine as electron donor, which provides the electrons for the reduction, and an organic solvent which also facilitates dissolution of CO2.The efficiency of (CO + H2) gas production and the selectivity CO/H2 markedly depend upon the composition of the medium, the nature of the tertiary amine, the solvent, and the ligand of the Co ions. 2,9-Dimethyl-1,10-phenanthroline is particularly effective in promoting CO and H2 formation, giving a quantum yield of 7.7percent in (CO + H2)(1.2percent for CO and 6.5percent for H2).The process consists of two catalytic cycles: a photocatalytic cycle for the Ru complex and a double dark reaction pathway for the Co species; oxidative and/or reductive quenching of the excited state of the photosensitizer lead to the formation of Co(I) species which reduce either CO2 or H2O to CO or H2, respectively.