| 摘要: | 本論文分成擔載銅觸媒和擔載金觸媒兩部份。 擔載銅觸媒部份： 本研究以稻殼為起始原料，經過水洗、酸洗、熱解及碳燒等處理程序，製成稻殼灰分，並以其為擔體，利用離子交換法製備成稻殼灰分擔體銅觸媒(簡稱為Cu/RHA觸媒)，也用相同方法製備商用氧化矽膠擔體銅觸媒(簡稱為Cu/SiO2觸媒)。配合物性檢測元素分析儀(EA)、感應耦合電漿原子放射光譜儀(ICP-AES)、氮吸附法、傅利葉轉換紅外線光譜儀(FTIR)、X射線繞射儀(XRD)、微分掃描熱分析儀(DSC)、X-Ray光電子光譜儀(XPS)、程式升溫還原(TPR)、N2O分解吸附(dissociative adsorption of nitrous oxide)及穿透式電子顯微鏡(TEM)等各項儀器與分析技術，分別對擔體及觸媒進行鑑定。然後以乙醇脫氫反應作為觸媒催化活性的測試，藉以評估稻殼灰分做為觸媒擔體的可行性。在稻殼灰分的組成分析方面，從分析結果得知：二氧化矽的純度達99 wt%，其晶態屬於非晶型的二氧化矽，氮吸附分析結果指出其BET比表面積約為153 m2/g，煅燒後的Cu/RHA觸媒，其BET比表面積隨銅金屬載量增加而增加。FTIR的分析結果顯示，利用離子交換法製備Cu/RHA觸媒，在煅燒前為類孔雀石結構。由XPS結果得知，煅燒後Cu/RHA觸媒表面存在氧化銅和Cu2+離子，在523 K下經氫氣還原氧化銅成Cu0或/和Cu+。TEM中看出銅晶粒呈圓形，在RHA表面上有高分散度。從TPR圖譜可看出，Cu/RHA觸媒在不同銅金屬載量下有相同的還原溫度，不同銅載量有相同的擔體效應。從XRD圖譜也可看出，銅粒徑隨著煅燒溫度的增加有增加的趨勢。Cu/RHA觸媒在483~573 K下進行乙醇脫氫反應，結果顯示，不同煅燒溫度對反應性影響不大，但隨銅載量的增加而稍微增加。比較Cu/RHA與Cu/SiO2觸媒的結果，Cu/RHA觸媒比Cu/SiO2觸媒有更高的活性和較低的活性衰退。 擔載金觸媒部份： 本研究利用共沈澱法製備Au/MnOx 和 Au/CuO/ZnO奈米金觸媒。配合物性檢測感應耦合電漿原子放射光譜儀(ICP-AES)、氮吸附法、X射線繞射儀(XRD)、熱重分析儀(TGA)、X-Ray光電子光譜儀(XPS)、穿透式電子顯微鏡(TEM)及掃描式電子顯微鏡(SEM)等各項儀器分析對觸媒進行鑑定。甲醇部份氧化反應作為觸媒催化活性的測試，藉以產製高純度氫氣，並比較Au/CuO/ZnO 觸媒和Au/ZnO、CuO/ZnO觸媒的活性。 在Au/MnOx觸媒方面，XRD和XPS結果顯示，未煅燒觸媒擔體是碳酸錳，金則呈氧化金和金屬態金共存。在573 K下煅燒，碳酸錳分解為Mn2O3，金則由氧化金分解為金屬態金。TEM圖片看出金晶粒呈圓形，增加煅燒溫度至873 K，金粒子從5.2 nm成長至7.5 nm。不同金載量、煅燒溫度和反應溫度會影響反應活性。以氫氣選擇率而言，最適當的金載量為1.9 at.%。未煅燒觸媒具有較高的甲醇轉化率和氫氣選擇率，隨著煅燒溫度增加而下降。未煅燒觸媒活性較高的原因是因為金晶粒較小，氧化金量較多，也存在較多的氫氧基。在反應溫度473~563 K下，甲醇轉化率和氫氣選擇率隨著反應溫度增加而增加，到了523 K 之後就趨於穩定。由不同反應溫度分析，在低溫下反應為甲醇部份氧化，在高溫為甲醇水汽重組反應。 在Au/CuO/ZnO觸媒，由TGA和XRD分析得觸媒主要由hydrozincite (Zn5(CO3)2(OH)6) 組成，次成分為aurichalcite (Zn3Cu2(CO3)2(OH)6)。隨著煅燒溫度提高，這二者分解成CuO和ZnO。 TEM結果得知，隨著煅燒溫度增加至673 K，金晶粒由2.5成長到13 nm。比較Au/CuO/ZnO和CuO/ZnO觸媒的TPR，金成分存在會使氧化銅還原成金屬銅的還原溫度偏向低溫。Au/CuO/ZnO、Au/ZnO和CuO/ZnO觸媒在523 K，進料O2/CH3OH為0.5下，進行甲醇部份氧化反應；Au/CuO/ZnO觸媒有較高的活性和氫氣選擇率，較少的一氧化碳產生，由XRD和TPR分析是由於Au/CuO/ZnO觸媒有氧化態金和還原態的銅存在，因此具有高活性。在不同煅燒溫度下比較，最適當的煅燒溫度為573 K。在不同反應溫度423~548 K下，Au/CuO/ZnO觸媒進行反應。反應溫度達448 K，氧氣轉化率就達100 %；升溫至498 K甲醇轉化率達100 %，一氧化碳的形成則是由甲醇熱分解所產生。與文獻上銅觸媒、鈀觸媒的催化結果做比較，金觸媒不僅催化活性高，產生的CO氣體量少。由此結果可看出奈米金觸媒對於催化甲醇部份氧化反應，能夠選擇性的抑制CO的產生，相信可應用在燃料電池的氫氣源供應上。 This thesis is divided into two parts. Part Ⅰ：Supported copper catalyst Samples of copper on rice husk ash (Cu/RHA) have been prepared by the ion exchange method, with various copper loadings and have been calcined at different temperatures. Such samples were tested for dehydrogenation of ethanol to acetaldehyde. The samples were characterized by DSC, XRD, FTIR, TEM, XPS, TPR, BET, and H2-N2O titration techniques. FTIR spectra of dried and calcined samples illustrate the formation of chrysocolla in Cu/RHA. XRD and XPS results of the calcined sample show the presence of two different species of copper, as CuO and as Cu2+ ions. Upon reduction in hydrogen above 523 K, the copper species are partially reduced to Cuo and/or Cu+. TEM images show that copper crystallites are spherical in shape and are evenly distributed. TPR results reveal that various copper loadings in Cu/RHA exhibit similar metal-support interaction (MSI). Ethanol conversion for dehydrogenation of ethanol is found to be independent with calcination temperature and has little effect on Cu loading. Ethanol is selectively converted to acetaldehyde at the reaction temperature of 483~573 K. The Cu/RHA exhibit higher catalytic activity and lower deactivation rate in comparison with Cu/SiO2 catalysts. Catalytic activity of Cu/RHA is found to depend on both Cu surface area and interaction of metal species with the support. Part Ⅱ：Supported gold catalyst Hydrogen production by partial oxidation of methanol, using air as oxidant, has been studied over a series of Au/MnOx and Au/CuO/ZnO catalysts, prepared by co-precipitation technique. The activity of Au/CuO/ZnO catalysts has been compared with Au/ZnO and CuO/ZnO catalysts.Catalyst characterization included ICP, TGA, TPR, BET, XRD, TEM and XPS analysis. In Au/MnOx catalysts, XRD and XPS analyses demonstrate that in uncalcined catalyst the support is present mainly as manganese carbonate and gold as both in metallic and oxidic form. After calcination at 573 K, the carbonate converted to oxides of manganese, mainly as Mn2O3 and oxidized Au phase is reduced to metallic gold. TEM analysis indicates that the manganese support is present as plate-like shape and the gold particles as spherical shape. The size of the gold particles increases from 5.2 nm to 7.5 nm when the calcination temperature increases up to 873 K. Different gold loading, calcination temperature and reaction temperature strongly influence the catalytic activity. The optimum gold content for hydrogen selectivity is 1.9 at.% Au. The uncalcined catalyst shows the highest activity and it decreases with increasing calcination temperature. The higher activity of uncalcined catalyst could be due to the presence of smaller metallic Au crystallites with partially oxidized Au and excess hydroxyl group. It appears plausible to suggest that pore size play a key role in determining the hydrogen selectivity. In the reaction temperature range of 473~563 K, both hydrogen selectivity and methanol conversion increase with increasing the temperature and reach a steady state at 523 K. The overall reaction consists of consecutive partial oxidation of methanol at low temperature and methanol steam reforming at high temperature. In Au/CuO/ZnO catalysts, TGA and XRD analyses demonstrate that the uncalcined Au/CuO/ZnO catalyst samples contain hydrozincite (Zn5(CO3)2(OH)6) and aurichalcite (Zn3Cu2(CO3)2(OH)6) as major components. They decompose into CuO and ZnO during the calcination procedure. TEM analysis reveals that the size of the gold particles increases from 2.5 to 13 nm with the rise in calcination temperature up to 673 K. TPR studies of the CuO/ZnO and Au/CuO/ZnO samples indicate that a shift to lower temperatures for the reduction of Cu2+ to metallic copper in the gold containing sample. This phenomenon is caused by an interaction between gold, CuO and ZnO. The catalytic activity of Au/CuO/ZnO, Au/ZnO and CuO/ZnO catalysts for the POM reaction was studied at 523 K using O2/CH3OH molar ratio of 0.5. The Au/CuO/ZnO catalysts are highly active for POM reaction to produce hydrogen with lesser amount of CO. The results obtained by XRD and TPR characterization indicate that oxidized gold species and reduced copper species in catalysts are active for high activity. The effect of calcination temperature on Au/CuO/ZnO performance shows that the ideal calcination temperature is 573 K. The effect of reaction temperature on catalytic performance of the Au/CuO/ZnO catalysts was studied in the temperature range of 423~548 K. At 448 K the reaction sets on and complete consumption of O2 is observed. Methanol conversion reaches 100 % at 498 K and hydrogen selectivity reaches 100 % at 523 K. CO formed by methanol decomposition is converted to CO2 leading to very low CO throughout the temperature range studied. Water formed by methanol combustion is consumed by steam reforming reaction at high reaction temperatures, leading to 100 % selectivity towards hydrogen formation. |
