Abstract
Crude sample of hydrated cobalt (III) oxide, Co2O3． H2O, has been prepared by oxidation of Co(OH)2 precipitates in aqueous solution with hydrogen peroxide. The oxidation state of prepared oxide has been characterized by the thermo-gravimetry (TG) and the temperature programmed reduction (TPR). TPR studies further indicated that the crude sample was contaminated with 4% CoO2 and that the reduction in TPR was proceeded in four distinguishable steps, i.e., CoO2 ® Co2O3 ® Co3O4 ® CoO ® Co, at reduction temperatures of Tr = 410, 480, 520 and 590 K, respectively. The meta-stable intermediates in this reduction sequence have been isolated and physically characterized by combined techniques of the X-ray diffraction (XRD), the infrared spectroscopy (IR), the X-ray photoelectron spectroscopy (XPS) and the X-ray absorption near edge spectroscopy (XANES). Among these techniques, TPR and XANES can provide the average oxidation state for cobalt in solid samples. In this study, a refined sample of cobalt (III) oxide, Co2O3．H2O, has been successfully prepared from a TPR reduction of the crude sample to 420 K. This oxide is thermally unstable at high temperature and tends to decompose into Co3O4 on calcinations at T > 670 K in air.