鉑合金觸媒的乙醇氧化反應機理之探討
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Date
2015
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Abstract
本論文以 Pt 3 Pd、Pt 3 Ag、Pt 3 Rh、Pt 3 Au、Pt 3 Cu、Pt 3 Ru 等五種合金觸媒與 Pt
金屬做比較在鹼性 KOH 溶液下對乙醇電氧化反應的產物做及時偵測,並將金屬
對乙醇的氧化反應機構做有系統的研究。
本實驗所用到的陽極合金觸媒皆是以乙二醇-硼酸還原法製備,以乙二醇以及
硼酸 NaBH 4 做為還原劑還原金屬並吸附在 Vulcan XC-72 碳黑上,此法合成出來
的樣品粉末會先以 XRD、SEM 與 EDX 測試鑑定其結構、組成、以及顆粒大小
等物理性質的鑑定,再將合成出來的金屬觸媒吸附在玻璃碳電極上進行電化學測
是。在本文中,電化學實驗是以循環伏安法以及計時安培法來測試得到金屬觸媒
的電化學性質、並將之分類。以循環伏安法在-0.9V~0.6V 掃描後,以 FT-IR 以及
GC 分析經由乙醇電氧化產生出來的乙酸、乙醛、以及 CO 2 等產物,並探討、歸
納合金觸媒對乙醇的電氧化反應趨勢。
乙醇氧化反應主要分成兩種反應路徑: (1)斷裂乙醇 C-C 鍵使 12 個電子轉移
的 C1 路徑以及 (2)氧化乙醇至乙酸產生 4 個電子的 C2 路徑。本研究中會將兩
種路徑的產物作分析,結果得知在低電位下(-0.9~0.6 V),Pt 3 Ag、Pt 3 Au 在做為觸
媒具有較高的電流密度,其電氧化效能是最好的。且其 FT-IR 以及 GC 的結果顯
示這兩種合金主要是以乙酸做為主要產物,推測這兩種合金是趨向 C2 路徑。而
Pt 3 Rh、Pt 3 Ru 在 GC 的研究中顯示這兩種的 CO 2 產量是最高的,推測這兩種合金
觸媒對乙醇氧化反應機構主要是走 C1 路徑。Pt 3 Pd、Pt 3 Cu 雖然其電化學效能最
差,但經由產物分析後得知這兩種合金主要也是 C2 路徑為主。
In this study, we systematically investigated ethanol oxidation reaction (EOR) on the six Pt alloys, Pt 3 Pd, Pt 3 Ag, Pt 3 Rh, Pt 3 Au, Pt 3 Cu and Pt 3 Ru, and pure Pt metals in alkaline (KOH) solution. The alloy and metallic electro-catalyst were prepared by the ethylene glycol-NaBH 4 reduction method and deposited on Vulcan XC-72. The electro-catalyst powders were initially characterized by SEM, EDX and XRD to confirm their crystal structures, chemical compositions and particle sizes. The electro-catalytic properties of the fabricated samples were further examined by cyclic voltammetry (CV) and chronoamperometry(CA). Products from EOR, including CO 2 , CO, CH 3 CHO and CH 3 COOH, on those samples were also studied by in situ FTIR and Gas Chromatography (GC). Combining the results from electrochemical measurements and product distributions, the mechanism of EOR on Pt-based alloys can be thoroughly understood. Our mechanistic results found that Pt 3 Ag and Pt 3 Au have better current density and the main products are acetic acid, indicating that EOR prefers 4-electron oxidation reaction forming C2 products on those alloys. EOR prefers 12-electron oxidation on Pt 3 Ru and Pt 3 Rh in the formation of CO 2 . Pt 3 Cu and Pt 3 Pd alloys have the worst electo-oxidation ability and through the pathway for C2 products.
In this study, we systematically investigated ethanol oxidation reaction (EOR) on the six Pt alloys, Pt 3 Pd, Pt 3 Ag, Pt 3 Rh, Pt 3 Au, Pt 3 Cu and Pt 3 Ru, and pure Pt metals in alkaline (KOH) solution. The alloy and metallic electro-catalyst were prepared by the ethylene glycol-NaBH 4 reduction method and deposited on Vulcan XC-72. The electro-catalyst powders were initially characterized by SEM, EDX and XRD to confirm their crystal structures, chemical compositions and particle sizes. The electro-catalytic properties of the fabricated samples were further examined by cyclic voltammetry (CV) and chronoamperometry(CA). Products from EOR, including CO 2 , CO, CH 3 CHO and CH 3 COOH, on those samples were also studied by in situ FTIR and Gas Chromatography (GC). Combining the results from electrochemical measurements and product distributions, the mechanism of EOR on Pt-based alloys can be thoroughly understood. Our mechanistic results found that Pt 3 Ag and Pt 3 Au have better current density and the main products are acetic acid, indicating that EOR prefers 4-electron oxidation reaction forming C2 products on those alloys. EOR prefers 12-electron oxidation on Pt 3 Ru and Pt 3 Rh in the formation of CO 2 . Pt 3 Cu and Pt 3 Pd alloys have the worst electo-oxidation ability and through the pathway for C2 products.
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Keywords
乙醇氧化反應, 即時性傅立葉紅外線光譜儀, 氣相層析, 合金觸媒, EOR, in situ FT-IR, GC, Pt alloy catalyst