Yin and Yang Dual Characters of CuOx Clusters for C-C Bond Oxidation Driven by Visible Light

Abstract

Selective cleavage of C-C bonds is pursued as a useful chemical transformation method in biomass utilization. Herein, we report a hybrid CuOx/ceria/anatase nanotube catalyst in the selective oxidation of C-C bonds under visible light irradiation. Using the lignin β-1 model as a substrate offers 96% yields of benzaldehydes. Characterization results by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy element (EDX) mapping reveal that CuOx clusters are highly dispersed on the exposed anatase surface as well as on the nanosized ceria domains. In-depth investigations by Raman and ultraviolet visible diffuse reflectance spectra (UV-vis DRS), together with density functional theory (DFT) calculations, further verify that the CuOx clusters present on the ceria domains increase the concentration of surface defects (Ce3+ ions and oxygen vacancies) and accordingly improve the photocatalytic activity (Yang character); the CuOx clusters decorating on anatase suppress the side reaction (oxy-dehydrogenation without C-C bond cleavage) because of an upward shift in the valence band (VB) edge of anatase (Yin character). Mechanism investigation indicates hydrogen abstraction from β-carbon by photogenerated holes is a vital step in the conversion.