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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/4010

    Title: 氧化矽-氧化鋅複合擔體銅觸媒應用於氧化性甲醇蒸氣重組產製氫氣之研究;Production of hydrogen by oxidative steam reforming of methanol over Cu/SiO2-ZnO catalyst
    Authors: 劉恭益;Kung-yi Liu
    Contributors: 化學工程與材料工程研究所
    Keywords: 銅觸媒;氫氣;複合擔體;hydrogen production;catalyst;OSRM
    Date: 2007-06-28
    Issue Date: 2009-09-21 12:28:25 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 本研究以銅為觸媒,氧化矽(SiO2)為主要擔體,採含浸法製備成複合擔體,複合物包括了:ZnO、ZrO2及Al2O3,目的在進行表面改質。接著利用沉澱固著法製備成複合擔體銅觸媒,並且進行氧化性甲醇蒸氣重組反應(oxidative steam reforming reaction,CH3OH + 0.5H2O+0.25O2 →2.5H2 + CO2 )產製氫氣的程序,此反應具有不錯的氫氣產生速率,以及相當低的CO選擇率,可避免CO濃度太高以致毒化燃料電池中的鉑電極。檢測儀器包括:感應耦合電漿質譜分析儀(ICP-MS)、熱重分析儀(TGA)、X射線繞射儀(XRD)、掃描式電子顯微鏡(SEM-EDS)、X射線光電子分析儀(XPS)、程式升溫還原(TPR)、N2O分解吸附(dissociative adsorption of nitrous oxide)等各項儀器與分析技術,分別對擔體及觸媒進行鑑定,藉以評估觸媒應用於質子交換膜燃料電池的可行性。 由XRD的結果看出Cu/SiO2-Al2O3觸媒的銅繞射峰最大,顯示Cu/SiO2-Al2O3觸媒的銅晶粒較大。由TPR的圖譜看出,Cu/SiO2-Al2O3觸媒的還原溫度最高,其次是Cu/SiO2-ZrO2,而Cu/SiO2-ZnO觸媒還原溫度最低,顯示添加Zn做為複合擔體可增加觸媒的還原性。由N2O分解吸附的結果顯示,Si/Zn原子比在8/2時有最佳的分散度及最小的粒徑,但是當Zn的量再增加至7/3時,銅晶粒反而變大。以沈澱固著法製備的Cu/SiO2-ZnO觸媒,由XPS的結果得知,在氧化性甲醇蒸氣重組反應,銅觸媒中Cu0最具有活性,優於氧化態的銅。由化學反應的活性測試發現,觸媒的活性與擔體複合物的選擇有關,其中以Cu/SiO2-ZnO的觸媒活性最佳,並且測得當Si/Zn的原子比為8/2的反應性最好。另外進料中氧與甲醇還有水與甲醇的比例也是影響反應的重要因素,當O2/CH3OH=0.3與H2O/CH3OH=1時,氫氣的產生速率最佳,一氧化碳的選擇率也較低。當反應溫度升高,一氧化碳的選擇率也隨之增高,會毒化燃料電池中的鉑電極,由結果得知最佳的反應溫度為250℃,具有高氫氣產生速率以及甲醇轉化率,一氧化碳的選擇率也很低。未來期望此銅觸媒能應用於燃料電池中,以產製高純度氫氣,作為燃料電池中的氫氣來源。 Selective production of hydrogen by oxidative steam reforming of methanol (CH3OH + 0.5H2O + 0.25O2-->2.5H2 + CO2) was investigated over Cu/SiO2-MOx (M=Zn, Zr and Al) catalysts. The catalyst preparation involves two steps. In the first step, the binary supports (SiO2-MOx) were prepared by incipient wetness impregnation method. In the second step, copper was supported on the binary support by deposition-precipitation technique. The catalysts were calcined at 673 K and finally reduced at 623 K. The catalysts were characterized by TGA, XRD, TPR, N2O titration, SEM-EDS and XPS analyses. The XRD analysis confirms the desired phase purity of ZnO, ZrO2 and Al2O3 samples and presence of metallic copper in all these catalysts. The TPR analysis illustrates that the reduction temperature for copper is higher in Cu/SiO2-Al2O3 catalyst than in Cu/SiO2-ZnO catalyst, which suggests that the presence of Zn to binary support could improve the catalytic reductive property. The studies on dissociate adsorption of nitrous oxide at various Si/Zn atomic ratios reveal that the catalyst with Si/Zn atomic ratio 8/2 exhibited better dispersion with smaller copper particle compared to the catalyst with Si/Zn atomic ratio 7/3. XPS analyses demonstrate that metallic copper in the catalysts are oxidized to Cu2O and CuO after catalytic tests. The catalytic activity of the catalysts for oxidative steam reforming of methanol to produce hydrogen depends strongly on the nature of the binary support, particle size and surface area of metallic copper. The activity of the copper catalysts supported on different binary supports shows that the Cu/SiO2-ZnO catalyst exhibited higher activity towards hydrogen formation compared to Cu/SiO2-ZrO2 and Cu/SiO2-Al2O3 catalysts. Since Cu/SiO2-ZnO catalyst showed higher catalytic activity for hydrogen formation, the activity of Cu/SiO2-ZnO catalyst were studied in detail at different Si/Zn atomic ratio, calcination temperature, O2/CH3OH molar ratio, H2O/CH3OH molar ratio and reaction temperature. The catalyst with Si/Zn atomic ratio 8/2 shows higher activity for methanol conversion and hydrogen production rate. The higher activity of the catalyst with Si/Zn atomic ratio 8/2 has been explained in terms of presence of highly dispersed small copper particle. The appropriate molar ratios of O2/CH3OH and H2O/CH3OH for the reaction are found to be 0.3 and 1, respectively. The optimum calcination temperature for OSRM is 673 K. The catalytic performance at various reaction temperatures shows that with increasing reaction temperatures from 473 to 573 K, methanol conversion increases from 15 to 95 % and hydrogen production rate increases from 0 to 269 mmol kg-1 s-1 and CO selectivity increases from 0.5 to 6.7 %. When the CO exceeds few ppm deactivates the Pt electrode, so the appropriate reaction temperature for OSRM is envisaged as 523 K, at which the methanol conversion is 95 % and hydrogen production rate is 287 mmol kg-1 s-1 and CO selectivity is 2.1 %. The present study proves that the Cu/SiO2-ZnO catalysts are active for OSRM that produce high hydrogen content with low carbon monoxide. Therefore, OSRM reaction over Cu/SiO2-ZnO catalyst to produce hydrogen for the application of fuel cells for electric-powered vehicles would be expected.
    Appears in Collections:[化學工程與材料工程研究所] 博碩士論文

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