Toward Visible-Light Photochemical CO2-to-CH4 Conversion in Aqueous Solutions Using Sensitized Molecular Catalysis

Solar fuels may be generated upon visible light induced catalytic reduction of carbon dioxide. This appealing approach remains highly challenging, especially when earth abundant catalysts, mild conditions, and water as a solvent were used. Employing an iron tetraphenyl porphyrin complex substituted by positively charged trimethylammonio groups at the para position of each phenyl ring and reduction with three electrons by the excited state of an iridium sensitizer (lambda > 420 nm) reduce CO2 to CO and to CH4 in both acetonitrile and aqueous solutions (acetonitrile/water 3:7 v:v) with good selectivity. Stability of the catalytic system remains a weakness and the reasons were analyzed.