| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 95 === The purpose of this research is to investigate catalysts with high CO conversion under low temperature water-gas shift reaction (WGSR).
According to the literature review, Au/CeO2 was one of the best choices since it could reach high CO conversion under low temperature WGSR. Therefore, Au/CeO2 is prepared by deposition-precipitation method (DP method) and several preparation factors listed below are systematically studied: (1) The preparation method of CeO2; (2) The pH value of gold solution; (3) The pH adjusting time of gold solution; (4) The method of the addition of NaOH(aq) into gold solution. Additionally, the performances as well as the properties of the catalysts which are prepared with different preparation conditions are all measured by WGSR and characterized by AA, ICP, BET surface area, HRTEM, XRD and XPS.
The experimental results indicate that the CeO2 with surface modification to pH=6 possesses the better performance; however, the CO conversion would decrease when the CeO2 with surface modification to pH=10 or without surface modification, and this is because the incomplete replacement of Cl－or the agglomeration of gold nanoparticles occurred in the latter two cases.
The better pH value for the gold solution is found to be 9 and this is the pH value corresponding to the state that the four Cl－ in the gold solution could be ideally replaced by the calculated amount of 0.1N NaOH(aq).
The proper pH adjusting time of gold solution is found to be 6h. The insufficient pH adjusting time would result in the incomplete replacement of Cl－; nevertheless, longer pH adjusting time would result in the aggregation of gold species. Both of the above-mentioned conditions possess negative effects toward the reactions.
As to the method of the addition of NaOH(aq) into gold solution, “Add NaOH(aq) into the gold solution at once in the beginning” is better than “Add NaOH(aq) into the gold solution gradually to keep specific pH value”. This is because more time and sufficient NaOH(aq) obtained in the former case would benefit to the occurance of completely replacement.
In this research, two reaction condition were applied:(1)CO/H2O/N2 = 2.65 /41.17/56.18；(2) CO/H2O/H2/CO2=2.65/41.17/44.94/11.24, total flow rate and reaction temperature of both conditions were 33.33ml/min and 200℃. The CO conversion of condition (1) was close to 100%, which is approaching the equilibrium conversion obtained from thermodynamics simulation; however, the CO conversion of condition (2) could only reach 75%, and this implies there is still much room to improve the performance in terms of the catalyst preparation process design.
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