Lawrence Berkeley National Laboratory

Hierarchical assembly of an oxo-bridged binuclear ZrOCoII light absorber unit coupled to a cuprous oxide nanocluster catalyst for CO2 reduction on mesoporous silica support is demonstrated. The proper positioning of the Cu oxide cluster was achieved by photodeposition of a [Cu(NCCH3)4]2+precursor by visible light excitation of the ZrOCo charge transfer chromophore, followed by mild calcination at 350 C. Illumination of the CuxOy-ZrOCo unit so formed in the presence of a diethylamine electron donor resulted in the reduction of surface Cu centers to Cu0 as demonstrated by the characteristic infrared band of adsorbed 13CO probe molecules at 2056 cm-1. For analogous CuxOy-TiOCoII units, the oxidation state makeup of the surface Cu centers was dominated by CuI, and the Cu0, CuI, and CuII composition was found to depend on the wavelength of MMCT excitation. The observed strong dependence of the CO2 photoreduction yield on the oxidation state of the surface Cu centers directly proves that CO2 is reduced on the CuxOy surface, thus establishing that the ZrOCoII unit functions as light absorber, donating electrons to the CuxOy catalyst on whose surface CO2 is reduced.