Directed Assembly of Cuprous Oxide Nanocatalyst for CO₂ Reduction Coupled to Heterobinuclear ZrOCo^II Light Absorber in Mesoporous Silica

Abstract

Hierarchical assembly of an oxo-bridged binuclear ZrOCo^II 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 Cu_<i>x</i>O_<i>y</i>-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 Cu_<i>x</i>O_<i>y</i>-TiOCo^II units, the oxidation state makeup of the surface Cu centers was dominated by Cu^I, and the Cu⁰, Cu^I, and Cu^II 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 Cu_<i>x</i>O_<i>y</i> surface, thus establishing that the ZrOCo^II unit functions as light absorber, donating electrons to the Cu_<i>x</i>O_<i>y</i> catalyst on whose surface CO₂ is reduced