Optical observation of oxidation and reduction of small supported copper particles

In situ and real-time optical absorption measurements of supported copper particles (4-10 nm) at wavelengths of 300 to 800 nm are carried out under H ₂, CO, and O ₂ respectively as ambient gases in the temperature range of 300 to 673 K. We observe a reversible change in the optical spectra caused by oxidation of copper and reduction of copper oxide. The data strongly indicate that the oxidation of small copper particles is composed of a fast process of Cu to CuO _x ( x ≈ 0.67) and a slow process of CuO _x ( x≈ 0.67) to CuO.