Photoreduction of CO2 and CO

Photoreduction of CO2 and CO using polypyridyl complexes is an area that has advancing significantly in the last few years. Several reduction reactions of CO2 are attractive on thermodynamic grounds in that the energy requirement per electron transfer is modest. Reduction of CO2 to CO, a two 

In practice complications associated with the multielectron nature of the reaction lead to direct electrochemical reduction occur at considerably more negative potentials (large overvoltages). One of the successful strategies of recent times has been to use redox catalysts, complexes of metal ions such as Re, Rh, Co or Ni that are capable of interacting directly with CO2 in their reduced state. 

Several light-induced electron transfer cycles using transition metal polypyridyl complexes that lead to catalytic fixation of CO2 or CO have been identified [69,70]. Visible light photolysis of C02-saturated aqueous acetonitrile solutions containing Ru(bpy)32+ (as photosensitizer), Co(II) ions (as the catalyst), 4,7-Me2-phenanthroline (as the ligand to complex the Co(II) in situ), triethanolamine (as donor) yields a mixture of CO and H2 (synthetic gas). The syn gas mixture is produced by simultaneous occurrence of two reduction reactions  

Related to the above are photocatalytic systems that can evolve H2 from water in the presence of CO as the reductant  

This reaction known as the water-gas shift reaction is an important step in any scheme for the utilization of coal and other carbon sources for liquid fuel 

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