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標題: | 表面電位於金/二氧化鈦製備程序對催化一氧化碳氧化之影響 Preparation of Au/TiO2 for CO Oxidation: Surface Charge Effect |
作者: | Yu-Hsiang Huang 黃昱翔 |
指導教授: | 萬本儒(Ben-Zu Wan) |
關鍵字: | 奈米金觸媒,二氧化鈦,表面電位,氯,製備程序,一氧化碳氧化反應, nano-gold,titania,zeta potential,chlorine,preparation procedure,CO oxidation, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 本研究利用沉積沉澱法將四氯金酸擔載於不同表面電位之二氧化鈦上,應用在常溫一氧化碳氧化反應。觸媒相關物化性質是由AA、HRTEM、XPS、XRD與Zeta Potential Analyzer等儀器鑑定。
Au/TiO2以四氯金酸做為前驅物,研究中控制金溶液之pH值來改變二氧化鈦擔體的表面電位,以探討對金負載量、奈米金催化活性、表面金的價態以及氯殘留量的影響。研究發現,未調整pH值之金溶液其pH值(e.g., pH=2.6)本來就低於二氧化鈦的等電位點(pH=7.5) ,直接使用就能使二氧化鈦表面電位為正,與溶液中帶負電的金前驅物(四氯金酸)有強烈庫侖吸引力,使金物種較容易的擔載在二氧化鈦上。由於殘留的氯離子會降低金觸媒活性,沉澱沉積程序後會以氫氧化鈉鹼液滴定將負載金觸媒之擔體懸浮液從pH 2.6調整至6,以置換觸媒上的氯離子為氫氧離子。然而本研究發現,強烈庫侖吸引力仍會使部份的氯離子無法被置換出來,使表面的金偏向氧化態,降低金觸媒的催化活性。若是在沉澱沉積前事先將金溶液以氫氧化鈉鹼液滴定,將pH值(pH=2.6)調整為6,然後才加入二氧化鈦進行沉澱沉積程序。研究結果發現雖然二氧化鈦表面在pH 6環境下已接近等電位點(較不帶電使庫侖吸引力較弱),致使金負載量較低,但是懸浮液中之金前驅物(四氯金酸)的氯在擔載前就已能有效被置換,因而降低二氧化鈦奈米金觸媒中氯的殘留,而能提高觸媒的催化活性及穩定性。本研究顯示二氧化鈦擔體表面電位以及沉澱沉積程序對奈米金觸媒有顯著影響,強烈庫侖吸引力利於沉澱沉積但不利於後處理程序中氯離子的置換。 研究中進一步討論製備程序對金觸媒反應活性的影響。觸媒製備程序中,金溶液調整後的pH值、載負溫度、去離子水洗及乾燥觸媒的方式等步驟是影響氯離子殘留、金顆粒載負和反應活性的主要製備變因,結果顯示,將金溶液調整pH值為6,並於80°C的溫度下進行沉積沉澱的程序,並經過60°C攪拌水洗的方式,最後於60°C飽和水蒸汽環境乾燥,能有效去除殘留在觸媒的氯離子,提升反應活性。 In this research, tetrachloroauric acid was loaded on titania with different zeta potentials by deposition-precipitation method and applied for carbon monoxide oxidation at room temperature. The properties of the catalysts were characterized by using various instruments such as AA, HRTEM, XPS, XRD and Zeta Potential Analyzer. Tetrachloroauric acid was used as a precursor for Au/TiO2. The pH of the gold solution was controlled to change the zeta potential of the titania, for investigating the effects on gold loading, the catalytic activity, the valence states of surface gold, and residual chlorine. It was found that pH of an unadjusted gold solution (e.g., pH=2.6) was much lower than the isoelectric point (IEP) of titania (pH=7.5), so that the surface potential of titania was positive when used directly. The Coulomb force resulted from the negatively charged gold precursor (tetrachloroauric acid) and the positively charged titania support was strong. Therefore, 86% gold in the solution can be deposited onto titania. Since the residual chloride ions decrease the activity of the gold catalyst, the suspension was adjusted from pH 2.6 to 6 after the deposition, by dropwise addition of sodium hydroxide in order to displace the chloride ions on the catalyst. However, it was found that the strong Coulomb force caused some of the chloride ions remained, resulting in substantial gold oxides on the surface and decreasing the catalytic activity. If the gold solution was previously titrated with sodium hydroxide before deposition process, meaning the pH was adjusted from 2.6 to 6 before titania was added to the solution for the deposition. The results confirm the lower gold loading, because the surface charge of titania is close to neutral and the weaker Coulomb force. However, chlorine ions can be effectively replaced before the deposition, thereby reducing the residual chlorine remaining on the catalysts, resulting in higher catalytic activity and higher stability. This study has shown that the zeta potential of titania support and Coulomb force in deposition-precipitation procedures have significant impacts on nano-gold catalyst. Coulomb force favors the deposition of gold but does not favor for the replacement of chloride ions in the post-treatment process. In the research, influence of preparation procedures on catalytic activity of Au/TiO2 were further studied. The effects of deposit temperature, the ways of washing, and the methods of drying for Au/TiO2 were investigated. It has been concluded that the gold solution adjusted to pH 6 for the deposition at 80°C,the filter cake washed in water at 60°C, and the solid dried in a saturated vapor atmosphere at 60°C, can effectively increase the catalytic activity of Au/TiO2 for CO oxidation. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/70592 |
DOI: | 10.6342/NTU201802987 |
全文授權: | 有償授權 |
顯示於系所單位: | 化學工程學系 |
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