Reduction of nanostructured CuO bundles: Correlation between microstructure and reduction properties

A high yield of nanostructured CuO bundles with different building blocks is successfully prepared through simple hydrothermal and thermal treatment methods. The microstructure of the as-synthesized samples is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N-2 physisorption, and IR spectra. The results show that the microstructure of the CuO bundles, such as different grain sizes, BET surface areas, pore sizes, defects and morphologies of building blocks can be obtained by different synthetic methods. Moreover, H-2-TPR and in situ XRD experiments are used to investigate the reduction properties of the nanostructured CuO bundles. It is found that there are two different reduction pathways involved in the reduction processes at 30 mL/min of 10 vol. % H-2/N-2: for the sample synthesized through the hydrothermal method (CuO-HT), all of the CuO is reduced directly to metallic Cu; however, for the sample synthesized through the thermal treatment method (CuO-TT), all of the CuO is reduced to Cu2O intermediate, then to metallic Cu, and the reduction temperature of the CuO-HT sample is much higher than that of the CuO-TT sample. These different reduction properties of the as-synthesized samples should be due to their different grain sizes, defect concentrations, and pore structures.