| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程研究所 === 93 === Fe2O3-supported Au catalysts (Au/Fe2O3) were prepared by the inverse co-precipitation method and Fe2O3-MOX composite oxides supported Au catalysts (Au/Fe2O3-MOX) were prepared by the deposition precipitation method. Gold on supported catalysts have been characterized by thermogravimetric analyzer (TGA), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), nitrogen adsorption method (BET) and inductively coupled plasma-atomic emission spectrometer (ICP-AES). In this work Au catalysts have been studied for the partial oxidation of methanol (POM) with oxygen to produce hydrogen.
For the Fe2O3-supported Au catalysts (Au/Fe2O3) system, XRD reveals an ultra fine crystallite structure and at 673 K calcined samples, the possibility of metallic Au incorporation into the α- Fe2O3 phase. From the image of TEM, Au/Fe2O3 exhibit the Au crystallites clearly and good dispersion. In BET analysis, the surface area of Au/Fe2O3 decreases with an increase in calcination temperature. XPS analyses demonstrate that in uncalcined catalysts gold existed in two different states i.e. metallic gold (Au0), non-metallic gold (Auδ+), in catalysts calcined at 673 K only in metallic state. In this work Au/Fe2O3 catalysts have been studied for the partial oxidation of methanol (POM) with oxygen to produce hydrogen at 483-563 K. The results indicate that the optimal preparation method and operating conditions are 0.82 wt% in Au loading, 673 K in calcination temperature, and 523 K in reaction temperature.
For the Fe2O3-MOX composite oxides supported Au catalysts (Au/Fe2O3-MOX) system, the peaks of metallic gold are not detected in XRD since Au particle size is too small. The image of TEM shows an acceptable homogeneous size distribution of Au. All the observed gold particles are very small, most of them in the range of 2-4 nm. The XPS results of Au/Fe2O3-Al2O3 catalyst show that partially oxidized gold species have the best catalytic performance. Measured activities in POM over Au/Fe2O3-MOX decrease in the following order: Al2O3 > ZrO2 > ZnO. It could be concluded that the catalytic activity of the gold/metal oxide catalysts depends strongly not only on the dispersion of the gold particles but also on the state of the gold and the structure of the supports. Both hydrogen selectivity and methanol conversion increases with increasing the reaction temperature. The reaction pathway is suggested to consist of consecutive methanol partial oxidation and methanol steam reforming. Comparing in Au, Cu and Pd catalysts in POM reaction, Au/Fe2O3-Al2O3 catalyst have the higher methanol conversion. Although the hydrogen selectivity is lower than above two, but only 2% CO present, regarding applied still has its feasibility to the proton exchange membrane fuel cell(PEMFC).
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