Work-function-tuned electronic effect of a solute metal in the particles of copper alloys and the thin layer of surface oxides, and its influence on the catalysis on selective aerobic oxidation of benzylic alcohols

Cu-based alloys catalyse selective aerobic oxidation of benzylic alcohols via their thin layers of surface oxides under mild conditions. The catalytic activity of Cu2O can be tuned by the work functions (ϕ) of both the solute metals and their oxides, of which the work functions of the oxides possess much more profound influence on the catalysis. [Display omitted] •Heterojunctions are formed between copper alloys and the thin layers of surface oxides and within the surface oxides layers.•At the thin layer of the surface oxides, the catalysis of aerobic oxidation of benzylic alcohols occurs.•The catalytic activity of the copper alloys varies with the solute metals.•The work functions of both the solute metals and their oxides can electronically tune the catalysis.•The work functions of the surface oxides influence the catalysis far more profoundly than those of the solute metals. In this work, four types of commercially available copper-based alloys, Cu-Ni-Zn, Cu-Zn, Cu-Pb-Sn and Cu-Sn were examined for their catalysis on selective aerobic oxidation of benzylic alcohols at 60 °C with N-methylimidazole (NMI) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as the co-catalysts in acetonitrile. It has been found that these solute metals exhibit various influences on the catalysis and such influences correlate to the work-functions of the solute metals and their surface oxides. The solute metals and their oxides of lower work functions (Sn and Zn) than Cu and Cu2O, respectively, can enhance the catalysis whereas Ni and NiO which possess quite larger work functions almost entirely jeopardize the catalysis. The electronic effect is conveyed through a three-ply structure, the bulky part of the alloy particles, Motty-Schottky junction and the surface oxides, of which the surface oxides affect much more profoundly the catalysis than the other two. The electronic effect is attributed to the band structure and internal electric field within the alloys caused by Fermi energy level alignment due to the difference in their work functions between Cu/Cu2O and M/MO (M = Sn, Zn, Pb and Ni). Moreover, the alloys exhibit much improved durability compared to either Cu or Cu2O, respectively.