氧化矽-氧化鋅複合擔體銅觸媒應用於甲醇部分氧化產製氫氣之研究; Production of hydrogen via partial oxidation of methanol over Cu/SiO2-Zno catalysts

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题名:	氧化矽-氧化鋅複合擔體銅觸媒應用於甲醇部分氧化產製氫氣之研究;Production of hydrogen via partial oxidation of methanol over Cu/SiO2-Zno catalysts
作者:	李澤安;Tse-An Lee
贡献者:	化學工程與材料工程研究所
关键词:	銅觸媒;複合擔體;甲醇部分氧化反應;製氫;沉澱固著法;hydrogen;partial oxidation of methanol;copper supported catalyst;Cu/SiO2-ZnO
日期:	2007-06-28
上传时间:	2009-09-21 12:28:30 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本研究探討選用SiO2-ZnO、SiO2-ZrO2、SiO2-Al2O3三種複合擔體製備擔載銅觸媒，應用於甲醇部分氧化反應產製氫氣(CH3OH+0.5O2→2H2+CO2)，藉以評估觸媒應用於質子交換膜燃料電池的可行性。觸媒製備先利用初濕含浸法製備SiO2-ZnO、SiO2-ZrO2、SiO2-Al2O3三種複合擔體，再利用沉澱固著法將銅負載於複合擔體上成為20wt% Cu/SiO2-ZnO、20wt% Cu/SiO2-ZrO2、20wt% Cu/SiO2-Al2O3三種觸媒。探討觸媒應用於甲醇部分氧化反應中的甲醇轉化率、氫氣選擇率及一氧化碳選擇率來探討觸媒活性優劣，並藉由量測儀器與分析技術探討觸媒的物性。藉由感應耦合電漿質譜分析儀（ICP-MS）量測銅的實際負載量，預期銅負載量20wt%之觸媒實際銅負載量約為16wt%。熱重分析儀（TGA）探討觸媒前趨物熱解情形因此決定煅燒溫度為673K。由程式升溫還原(TPR)探討觸媒的擔體效應及還原特性，結果顯示Cu/SiO2-ZnO 觸媒有較強的擔體效應。X-ray繞射儀（XRD）分析反應前後觸媒的價電子態，判斷甲醇部分氧化反應的觸媒活性點為零價態的金屬銅。藉由X-ray光電子分析儀(XPS)證實Cu/SiO2-ZnO觸媒經氫氣於600K還原一小時後能將觸媒上之氧化銅還原成零價態的金屬銅。由N2O分解吸附法(dissociative adsorption of nitrous oxide)量測銅金屬表面積及分散度，結果顯示SiO2擔體本身即提供銅高比表面積，添加ZnO為複合擔體並無法再增加銅比表面積。接著由甲醇部分氧化反應探討複合擔體相對量、觸媒煅燒溫度、O2/CH3OH反應物進料比及反應溫度等變因對反應的影響。實驗結果顯示20wt% Cu/SiO2-ZnO (Si/Zn=9/1)觸媒於673K煅燒及600K還原後、進料比O2/CH3OH=0.5、反應溫度523K等條件下對甲醇部分氧化反應有較佳的甲醇轉化率及氫氣選擇率。藉由物性及化性結果顯示添加ZnO為複合擔體之Cu/SiO2-ZnO觸媒能抑制觸媒於反應過程中產生的失活現象，並提供觸媒穩定性及產生較多的氫氣。 Copper supported on three different binary supports such as SiO2-ZnO, SiO2-ZrO2 and SiO2-Al2O3 were tested for partial oxidation of methanol (CH3OH + 0.5 O2 -> 2H2 + CO2) to produce hydrogen for fuel cell application. The activity of these catalysts was compared with Cu/SiO2 catalyst. The reaction parameters such as calcination temperature, O2/CH3OH molar ratio and reaction temperature were optimized. The catalyst preparation involves two steps. In the first step, the binary supports were prepared by incipient wetness impregnation method. In the second step, copper was supported on the binary support and the SiO2 support by deposition-precipitation technique. The catalysts were characterized by ICP-MS, TGA, XRD, TPR, N2O chemisorption and XPS analyses. ICP-MS analysis shows that with an initial copper loading of 20 wt % gives an actual loading of 16 wt% in the supported copper catalysts. TGA analysis signifies that minimum temperature required for decomposition of the catalyst precursor is 673 K. TPR analysis illustrates that reduction temperature of copper in Cu/SiO2-ZnO is shifted to higher value compared to that in the case of Cu/SiO2 catalyst. This shows a strong interaction between copper metal and the binary support compared to the single support. XRD and XPS analyses indicate that copper reduced to metallic copper (Cu0) under the flow of hydrogen at 600 K. The catalyst after catalytic test shows that the metallic copper species are partially oxidized to CuO and Cu2O species. N2O chemisorption analysis indicates that copper supported on the single and binary supports have similar copper surface area and copper dispersion. Therefore by adding additional support does not increase the specific copper surface area. Catalytic activity towards hydrogen formation shows that copper catalyst supported on the binary support, SiO2-ZnO is more active than copper supported on the single support, i.e., Cu/SiO2 catalyst. Moreover, the binary supported catalysts shows higher stability compared to the copper catalyst supported on the single support. The improved activity and stability of the binary supported catalysts has been explained in terms of strong interaction between the copper metal and the support. The measured activity for partial oxidation of methanol is decreased in this order: Cu/SiO2-ZnO > Cu/SiO2-ZrO2 = Cu/SiO2 > Cu/SiO2-Al2O3. The catalytic activity is found to be dependant on the partial pressure of oxygen, wherein the molar ratio O2/CH3OH =0.5 resulted in higher methanol conversion and higher hydrogen selectivity with lower carbon monoxide selectivity.
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