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體金觸媒(簡稱為Au/γ- Al2O3觸媒)，同時利用感應耦合電漿原子放射光譜儀(ICP-AES)、氮吸附法、熱重分析(TGA)、X射線繞射分析儀(XRD)、掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)、X-射線光電子分析儀(XPS)等各項儀器與分析技術，分別對擔體及觸媒進行鑑定，並利用甲醇部份氧化反應為為催化活性的測試，藉以評估奈米氧化鋁擔體金觸媒應用於質子交換膜燃料電池(PEMFC)的可行性。由ICP-AES 分析結果，顯示Au/γ- Al2O3觸媒的金載量取決於pH值及製備時氯化金溶液的濃度，在低於等電位點金可達到60 %；氮吸附分析指出，以沈澱固著法製備的Au/γ- Al2O3觸媒，BET比表面積幾乎不會受煅燒溫度及載量的影響。從XRD圖譜中，可發現不同沈澱劑所形成不同大小的金晶粒。從TEM分析結果，發現Au/γ- Al2O3觸媒製備時pH值若超過等電位點時，可形成金晶粒大小約4 nm，且均勻分散在擔體表面上。而XPS分析結果可發現，以沈澱固著法所製備的Au/γ- Al2O3觸媒，表面會形成氫氧化金沈澱，且隨著煅燒溫度的增加，會逐漸熱解成金屬態的金。經過反應活性的測試，我們找出最佳的操作變數為金載量需小於1 wt%、製備pH值為9、沈澱劑為Na2CO3、煅燒溫度為573 K。若以此條件所製備出的觸媒，於523 K下進行甲醇部份氧化反應，能得到最佳的甲醇轉化率與氫氣選擇率。與文獻上銅觸媒、鈀觸媒的催化結果做比較，Au/γ- Al2O3觸媒不僅催化活性高，且幾乎沒有CO氣體的產生。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。 In this work, γ-Al2O3 was used as a catalyst support. Nanosized Au/γ-Al2O3 catalysts were prepared by the deposition-precipitation method. The supported Au catalysts were characterized by inductively coupled plasma-atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD), thermogravimetric analyzer(TGA), nitrogen adsorption method , scanning electron microcopy (SEM), transmission elecron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The ICP-AES analysis indicates that gold loading is significantly affected by the preparation pH value. When the pH value is below isoelectric point of support precipitates reach 60% loading. The nitrogen adsorption analysis shows that the catalyst preparation procedure does not affect the surface area of the support. Furthermore , the TEM analysis demonstrates that the mean size of gold crystallites decreases with increasing pH value. Au/γ-Al2O3 catalysts was tested by the partial oxidation of methanol at 503-563K. The results indicate that the optimal preparations and operating conditions for best methanol conversion and hydrogen selectivity are 0.15 wt% in gold loading, 673 K in calcinations temperature, Na2CO3 in precipitation reagent, pH value 9 in prepared condition and 563K in reaction temperature. Moreover, compare to copper and palladium catalysts in POM reaction, Au/γ-Al2O3catalysts display good activity and highly CO selectivity. Nanosized Au/γ-Al2O3 catalysts may have an opportunity to apply in proton exchange membrane fuel cell.
