Photochemical and Electrochemical Reduction of Carbon Dioxide Catalyzed by a Polyoxometalate-Organic Photosensitizer Complex
A manganese substituted Anderson type polyoxometalate, [MnMo6O24]9-, tethered with an anthracene photosensitizer was prepared and used as catalyst for CO2 reduction. The polyoxometalate-photosensitizer hybrid complex, obtained by covalent attachment of the sensitizer to only one face of the planar polyoxometalate, was characterized by NMR, IR and mass spectroscopy. Cyclic voltammetry measurements show a catalytic response for the reduction of carbon dioxide, thereby suggesting catalysis at the manganese site on the open face of the polyoxometalate. Controlled potentiometric electrolysis showed the reduction of CO2 to CO with a TOF of ~15 sec-1. Further photochemical reactions showed that the polyoxometalate-anthracene hybrid complex was active for the reduction of CO2 to yield formic acid and/or CO in varying amounts dependent on the reducing agent used. Control experiments showed that the attachment of the photosensitizer to [MnMo6O24]9- is necessary for photocatalysis.