| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程研究所 === 98 === Nanosized gold catalyst has been reported to be a good catalyst for the liquid phase hydrogenation reactions due to their excellent activity and selectivity. In this research, two investigations were carried out on the gold catalyst: the affection of cobalt oxides and palladium to gold catalysts. A series of Au catalysts supported on CoOx-TiO2 with various Co contents were prepared. CoOx-TiO2 support was prepared by incipient-wetness impregnation with aqueous solution of Co(NO3)2 on TiO2. Gold catalysts were prepared by deposition-precipitation method (DP) with 1 wt. % Au loading. The molar rations of Co to Ti were 0, 1/99, 6/94, 1/9, 2/8, 3/7 and 1.0, respectively. The catalysts were denoted as Au/CoOx-TiO2 (m), where m represented the atomic ratio of Co/Ti. Palladium was added as a second metal on TiO2 which were prepared by impregnation with aqueous solution of Pd(NO3)2. Gold catalysts were prepared by deposition-precipitation method (DP) with 1 wt. % Au loading. After preparation, the catalysts were reduced under H2 at 423oC for 2h and reduced by sodium borohydride in the methanolic solution (50/50 methanol/water) at 298K under vigorous stirring and used nitrogen stream to remove air.
These catalysts were characterized by inductively-coupled-plasma-mass spectrometry (ICP-MS), X–ray diffraction (XRD), transmission electron microscopy(TEM), high resolution transmission electron microscopy(HR-TEM), X-ray photoelectron spectroscopy(XPS) and temperature programmed reduction (TPR). The catalytic properties of gold based catalysts were studied on hydrogenation of p–chloronitrobenzene (p-CNB). The conditions for hydrogenation reaction were 1.2 MPa H2 pressure, 353 K reaction temperature and 500 rpm stirring speed. Methanol was used as the solvent, the concentration of p-CNB was 0.2 M (2.54g p–CNB in 80 ml methanol) and the amount of gold based catalyst was 0.5g. The cobalt oxide in Au/CoOx-TiO2 plays the role of a textural promoter, prevents from sintering of gold particle, increased active sites, and then enhanced catalytic activity. Cobalt not only good in steric effect, but also be an electronic promoter, which donated partial electronic to Au. Au/CoOx-TiO2 (1:9) exhibited the highest activity among the series of Au/CoOx-TiO2. The Au-Pd/TiO2 catalyst which reduced by NaBH4 could reached 100% conversion at 180 min reaction time. The results showed that NaBH4 reduction could prevent Au0 from being oxidized, increased the active site. It could be concluded that suitable cobalt amount shows the best performance, and palladium could promote the conversion effectively.
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