機理性地探討甲醇及乙醇氧化反應於鉑二元與鉑錫三元 (銀、銅、釕)合金觸媒

此次研究主要探討甲醇及乙醇氧化反應（MOR/EOR）作用於碳黑XC-72上的金屬觸媒PtM/PtSnM（M = Ag，Cu，Ru）。所有合金觸媒都以含浸法合成，利用能量色散X射線光譜儀 (EDS)、粉末式X光繞射分析儀 (XRD) 及X光光電子光譜儀 (XPS) 來分別鑑定元素組成，晶格結構和各金屬氧化態。電化學實驗以循環伏安法 (CV) 檢測甲醇、乙醇氧化反應 (MOR/EOR) 活性以及合成的催化劑反應活性面積 (ECSA) ，而以計時電流法（CA）檢測合成的催化劑的穩定性。此外，我們採用傅立葉轉換紅外光譜儀 (FTIR) 來研究反應中產生的中間體和產物，以便了解其反應機制。在我們的電化學結果中可以發現Pt3Ag1Sn1具有最佳的MOR活性，但穩定性不佳。Ag的加入改變Pt表面的電子結構，讓甲醇的第一步反應快速進行，但是中間產物CO的脫附反而難以執行；Sn的加入能夠利用其吸附的氧來加速氧化中間產物，釋放活性表面，提升觸媒穩定性。而Pt3Ag1Sn1具有最佳的EOR活性和穩定性，Ag的加入改變Pt表面的電子結構，加強了EOR中的C2路徑反應，不易產生毒化表面的CO吸附，並且產生更強的反應電流；而Sn的加入提高了親氧性，加速了反應的進行，但其對穩定性的正面影響並不明顯。另外利用傅立葉轉換紅外光譜 (FTIR)來判別金屬觸媒的MOR/EOR反應機制，加入不同過渡金屬後產生反應路徑的變化是影響金屬觸媒的MOR/EOR 活性及穩定性的重點。MOR反應中的主要產物為甲醛及甲酸在各觸媒中都有發現；而各觸媒在EOR反應中主要的產物為乙酸，在各觸媒中以C2為主要反應路徑。而不論在MOR或EOR的IR結果中，產物產量最高的觸媒都是Pt3Ag1Sn1。

關鍵字

甲醇及乙醇氧化；電化學；鉑；錫；三元合金； XPS

並列摘要

The present work mechanistically investigates the methanol and ethanol oxidation reactions (MOR and EOR) on carbon supported Pt3M1 bimetallic and Pt3Sn1M1 trimetallic (M = Ag, Cu and Ru) catalysts. The samples were fabricated by impregnation method and characterized by Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) for their chemical composition, lattice constants and surface composition/oxidation states, respectively. The electrochemical active surface area (ECSA) and MOR/EOR performance were examined by cyclic voltammetry (CV); their durability were tested by chronoamperometry (CA). Also, the key intermediates during the electrochemical reactions were monitors by Fourier transfer infrared spectroscopy (FTIR) to assist the mechanism study. Pt3Sn1Ag1 has the best electrochemical performance with highest mass and specific activities (MA and SA) as well as the lower onset potential among the bimetallic catalysts, attributable to the enlarged lattice and less oxidized surface Pt upon Ag addition to assist the initial step in the electroxidation reaction. However, the stability is harmed by the retarded CO desorption in MOR. Similarly, Pt3Sn1Ag1 has the best electrochemical performance among the trimetallic catalysts; the addition of oxophilic Sn can further assist the oxidation of poisoning CO to enhance the stability. The FTIR results found that the main products of MOR are formaldehyde and formic acid in the 2 and 4-electron oxidation process; similarly, EOR mainly follows the C2 reaction pathway forming acetaldehyde and acetic acid, which is more abundant. Consistently, Pt3Sn1Ag1 shows the highest yields of those products in both MOR and EOR.