Widely Controllable Syngas Production by a Dye-Sensitized TiO2 Hybrid System with ReI and CoIII Catalysts under Visible-Light Irradiation

Visible-light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H-2 evolving Co-III catalyst and a CO-producing Re-I catalyst on TiO2 have been found to produce both H-2 and CO (syngas) in CO2-saturated N, N-dimethyl formamide (DMF)/water solution containing a 0.1M sacrificial electron donor. The H-2/CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the ReI and CoIII catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO2 to each of the CO2-reduction and hydrogen-evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.