氧化鋅促進劑對氧化鋁擔載奈米金觸媒 表面特性與催化活性之影響研究 ;Hydrogen production by partial oxidation of methanol over ZnO-promoted Au/Al2O3 catalysts

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Title:	氧化鋅促進劑對氧化鋁擔載奈米金觸媒表面特性與催化活性之影響研究;Hydrogen production by partial oxidation of methanol over ZnO-promoted Au/Al2O3 catalysts
Authors:	賴思嘉;Szu-Chia Lai
Contributors:	化學工程與材料工程研究所
Keywords:	甲醇部分氧化反應;氧化鋅促進劑;氧化鋁擔載奈米金觸媒;沈澱固著法;DP method;Au/ZnO/Al2O3 catalysts;POM reaction
Date:	2006-06-28
Issue Date:	2009-09-21 12:26:48 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本研究以氧化鋁為擔體，利用沈澱固著法製備成奈米氧化鋁擔載金觸媒（Au/Al2O3 觸媒），以及添加不同比例ZnO促進劑的擔載金觸媒（Au/ZnO/Al2O3觸媒），進行甲醇部分氧化反應（CH3OH + 1/2O2 → 2H2 + CO2）製備氫氣做為活性測試。利用感應耦合電漿原子發射光譜儀（ICP-AES）、熱重分析儀（TGA）、X射線繞射儀（XRD）、穿透式電子顯微鏡（TEM）、掃瞄式電子顯微鏡（SEM）等各項儀器與分析技術，分別對擔體及觸媒進行鑑定。從TEM的分析結果發現，以沈澱固著法製備出的Au/Al2O3和Au/ZnO/Al2O3觸媒，金晶粒均呈圓球型，直接吸附在擔體上。Au/ZnO/Al2O3觸媒中金顆粒的大小會隨著煅燒溫度而改變，未煅燒時金顆粒為3.0 nm，在873 K下煅燒後，Au顆粒則為8.8 nm，與Au/Al2O3 觸媒金晶粒相比，有明顯防止燒結功能。經過活性測試後發現，在pH＝8製備的觸媒，煅燒573 K的Au/ZnO/Al2O3觸媒有最佳的甲醇轉化率和氫氣選擇率。另外促進劑ZnO的添加比例也是影響反應的一個因素，以Au/Zn 原子比1/5的Au/ZnO/Al2O3觸媒有最高氫氣選擇率，和最低一氧化碳選擇率。隨著反應溫度的增加，甲醇轉化率和氫氣選擇率亦隨之增加。最後和文獻上的銅、鈀以及鉑觸媒催化結果做比較，Au/ZnO/Al2O3觸媒的催化活性較佳，CO的產率也較低，但是由於副產物HCOOCH3與CH4的生成，會降低甲醇部分氧化反應的氫氣選擇率，因此未來仍須進行觸媒的再改質，期望能提升氫氣選擇率，降低反應副產物的生成，以應用於燃料電池電動車上。 Au/Al2O3 and ZnO-promoted Au/ZnO/Al2O3 gold catalysts, prepared by the method of deposition-precipitation, were tested by partial oxidation of methanol (CH3OH + 1/2O2 → 2H2 + CO2) to produce hydrogen. The catalysts were characterized by ICP-AES, TGA, XRD, and TEM analyses. For XRD analyses, both gold catalysts had patterns similar to the aluminum support. No metallic Au peaks were observed; this is probably due to the small particle size of the gold loading. After calcination at 673 and 873 K, the appearance of Au(2 0 0) reflections becomes more visible. The appearance of gold reflection at higher temperature of calcination is interpreted as due to a higher average gold particle size. From TEM result, the gold species in Au/Al2O3 catalyst display spherical shapes and are distributed uniformly over the aluminum support. The mean particle size of gold increases from 3.0 to 8.8 nm, when the calcination temperature increases from 373 to 873 K. TEM observations show that the Au/ZnO/Al2O3 catalysts exhibit hemispherical gold particles, which are strongly attached to metal oxide support at their flat planes. The Au/ZnO/Al2O3 catalyst before POM shows that gold particles are regularly distributed on the whole support and after POM reaction at 548 K for 180 min shows that small gold particles initially present on catalysts are disappeared. The catalytic activity relates to the gold particle size, with smaller particles produce higher hydrogen selectivity. The catalyst precipitated at pH 8 and calcined at 573K shows highest activity for hydrogen generation. Besides, the promoter amount was a factor influenced the reaction. It also shows that the Au/Zn molar ratio of 1/5 has the highest methanol conversion and hydrogen selectivity. When the reaction temperature up to 548 K, the hydrogen selectivity increases with the increase of temperature, and that the selectivity of carbon monoxide decreases.
Appears in Collections:	[National Central University Department of Chemical & Materials Engineering] Electronic Thesis & Dissertation

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