| Summary: | 碩士 === 國防大學中正理工學院 === 應用化學研究所 === 90 === A mixed cobalt oxide, CoOx, was prepared from cobalt nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoOx by controlled hydrogen reduction in TPR to 170, 230 and 300 °C, respectively. They were characterized by thermogravimetry (TG), temperature programmed reduction (TPR), X-ray diffraction (XRD) and Fourier transform infrared (FTIR). Based on the characterization of CoOx with XRD and TPR, the major composition of CoOx is CoO(OH) and contains little Co4+ species. The thermal stability of the CoOx under nitrogen analysis with TG and characterization with XRD and IR indicates that the CoOx undergoes changes in its composition and structure according to: CoOx ® Co3O4 ® CoO. TPR experiments indicated that the reducibility of the CoOx followed four consecutive steps according to: CoOx ® CoO(OH) ® Co3O4 ® CoO ® Co. Adsorption of carbon monoxide (CO) and the co-adsorption of (CO + O2) over cobalt oxide was further tested by in situ diffuse reflectance FTIR. It shows that Co3O4 is quite active for the oxidation of CO at room temperature in the presence of oxygen, leading to the formation of CO2.
High surface area MCM-41 with mesoporous structure was used as support materials for Co(NO3)2 in the preparation of supported cobalt samples. Two different prepared methods were used : direct hydrothermal synthesis and incipient wetness impregnation for various loadings of cobalt. These samples were characterized by XRD, BET, TPR, XPS and TEM.
The XRD and BET study revealed that the wall thickness is : directed synthesis samples ＞ impregnated samples ＞ MCM-41 . The BET surface analysis shows that the surface area of directed synthesis samples was about the same with MCM-41 around 1000 m2/g and decreased by the addition of Co . The impregnated samples were the same .The TPR study showed that directed synthesis samples are easily to reduction, the reduction temperature is lower than impregnated samples almost 100 oC. The XPS study revealed that the binding energy (BE) of Co 2p3/2 and Co 2p1/2 peaks of impregnated samples are 779.9 and 795 eV , the estimated 2p3/2—2p1/2 spin orbitat spiltting is 15.1 eV , is the same with Co3O4. But the binding energy (BE) of Co 2p3/2 and Co 2p1/2 peaks of the directed synthesis samples is 798.3 and 782.5 eV , and spin orbital spiltting is 15.8 eV, is different to impregnated samples. TEM analysis shows that the cobalt oxide particles do distribute homogeneous in MCM-41 structure, especially in directed synthesis samples.
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