氧化鐵和氧化鐵-金屬氧化物擔載奈米金觸媒之製備與應用研究; Partial oxidation of methanol over Au/Fe2O3 and Au/Fe2O3-MOX catalyst

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題名:	氧化鐵和氧化鐵-金屬氧化物擔載奈米金觸媒之製備與應用研究;Partial oxidation of methanol over Au/Fe2O3 and Au/Fe2O3-MOX catalyst
作者:	廖麗美;Li-Mei Liao
貢獻者:	化學工程與材料工程研究所
關鍵詞:	金觸媒;氧化鐵;Composite oxides support;Gold catalyst;Partial
日期:	2005-06-28
上傳時間:	2009-09-21 12:25:34 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本研究分別以Fe2O3及Fe2O3-MOX(M=Al、Zr及Zn)為擔體，利用逆向共沉澱法製備氧化鐵擔體奈米金觸媒(簡稱為Au/Fe2O3觸媒)，以含浸和沉澱固著法製備複合擔體奈米金觸媒(簡稱Au/Fe2O3-MOX觸媒，M=Al、Zr及Zn)；同時利用感應耦合電漿原子放射光譜儀(ICP-AES)、BET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)和X-射線光電子光譜儀(XPS)等儀器進行擔體及觸媒特性分析，並利用甲醇部份氧化反應(POM)進行催化活性測試以產製高純度氫氣，藉以評估金觸媒應用於燃料電池的可行性。在氧化鐵擔載奈米金觸媒(Au/Fe2O3)方面，實驗結果發現：由氮吸附分析指出，煅燒溫度增加會使Au/Fe2O3觸媒孔道崩解，使BET比表面積下降。XRD圖譜顯示，Au/Fe2O3觸媒僅在高載量、極高煅燒溫度才能發現金的繞射峰。TEM分析結果發現Au/Fe2O3觸媒在高載量時金晶粒有聚集的現象，使用不同沉澱劑也會影響金粒大小，以Na2CO3為沉澱劑可形成最小金晶粒約4 nm，且均勻分散在擔體表面上。而XPS分析結果可發現，Au/Fe2O3觸媒，表面存在不同的金價態，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，我們發現Au/Fe2O3觸媒最佳的操作參數為金載量1 wt%、以Na2CO3為沉澱劑、煅燒溫度在673 K。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，能得到最高的甲醇轉化率與氫氣選擇率，Au/Fe2O3觸媒雖然催化活性高，卻仍然有CO氣體的產生。在氧化鐵-金屬氧化物擔載奈米金觸媒(Au/Fe2O3-Al2O3)方面，實驗結果發現：Au/Fe2O3-MOX(M=Al、Zr及Zn)觸媒因使用二元氧化物為擔體，穩定度高，因此增加煅燒溫度其比表面積變化不大。XRD圖譜顯示，複合擔體金觸媒因為金顆粒小於XRD偵測極限(5nm)，所以無法看到金。從TEM分析結果，發現Au/Fe2O3-MOX(M=Al、Zr及Zn)觸媒因為添加另一氧化物而改變擔體特性，可得較小的金顆粒(3nm)附著於擔體上。XPS分析結果可發現，Au/Fe2O3-MOX(M=Al、Zr及Zn)觸媒因沉澱固著法，表面形成氫氧化金，同樣因為煅燒使其轉變成氧化態金。經過反應活性的測試，最佳二元氧化物擔載奈米金觸媒為Au/Fe2O3-Al2O3，且煅燒前觸媒可得最佳催化活性。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，能得到最高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/Fe2O3-Al2O3不但具有極高的催化活性，CO的產量大幅降低(小於2%)。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。 Fe2O3-supported Au catalysts (Au/Fe2O3) were prepared by the inverse co-precipitation method and Fe2O3-MOX composite oxides supported Au catalysts (Au/Fe2O3-MOX) were prepared by the deposition precipitation method. Gold on supported catalysts have been characterized by thermogravimetric analyzer (TGA), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), nitrogen adsorption method (BET) and inductively coupled plasma-atomic emission spectrometer (ICP-AES). In this work Au catalysts have been studied for the partial oxidation of methanol (POM) with oxygen to produce hydrogen. For the Fe2O3-supported Au catalysts (Au/Fe2O3) system, XRD reveals an ultra fine crystallite structure and at 673 K calcined samples, the possibility of metallic Au incorporation into the α- Fe2O3 phase. From the image of TEM, Au/Fe2O3 exhibit the Au crystallites clearly and good dispersion. In BET analysis, the surface area of Au/Fe2O3 decreases with an increase in calcination temperature. XPS analyses demonstrate that in uncalcined catalysts gold existed in two different states i.e. metallic gold (Au0), non-metallic gold (Auδ+), in catalysts calcined at 673 K only in metallic state. In this work Au/Fe2O3 catalysts have been studied for the partial oxidation of methanol (POM) with oxygen to produce hydrogen at 483-563 K. The results indicate that the optimal preparation method and operating conditions are 0.82 wt% in Au loading, 673 K in calcination temperature, and 523 K in reaction temperature. For the Fe2O3-MOX composite oxides supported Au catalysts (Au/Fe2O3-MOX) system, the peaks of metallic gold are not detected in XRD since Au particle size is too small. The image of TEM shows an acceptable homogeneous size distribution of Au. All the observed gold particles are very small, most of them in the range of 2-4 nm. The XPS results of Au/Fe2O3-Al2O3 catalyst show that partially oxidized gold species have the best catalytic performance. Measured activities in POM over Au/Fe2O3-MOX decrease in the following order: Al2O3 > ZrO2 > ZnO. It could be concluded that the catalytic activity of the gold/metal oxide catalysts depends strongly not only on the dispersion of the gold particles but also on the state of the gold and the structure of the supports. Both hydrogen selectivity and methanol conversion increases with increasing the reaction temperature. The reaction pathway is suggested to consist of consecutive methanol partial oxidation and methanol steam reforming. Comparing in Au, Cu and Pd catalysts in POM reaction, Au/Fe2O3-Al2O3 catalyst have the higher methanol conversion. Although the hydrogen selectivity is lower than above two, but only 2% CO present, regarding applied still has its feasibility to the proton exchange membrane fuel cell(PEMFC).
顯示於類別:	[化學工程與材料工程研究所] 博碩士論文

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