乙醇電氧化在過渡金屬觸媒上之反應趨勢

Abstract

本論文以Pt、Pd、Rh、Ir、Au、Ag、Cu、Co與Ni等九種過渡金屬觸媒，在鹼性條件下對乙醇電氧化反應之產物，做有系統的研究。 上述九種金屬觸媒以含浸還原法製備，加入NaBH4當作還原劑，使其還原並吸附在Vulcan XC-72上。此法合成出來的樣品粉末，會先經由XRD、SEM、EDS與TEM的測試，藉此確認其結構、組成以及顆粒的大小，接著把合成出來的金屬觸媒，吸附到玻璃碳電極上進行電化學測試。本文採循環伏安法進行測試，從其實驗結果中找出各金屬觸媒的電化學特性，並依其性質將之分類；實驗以循環伏安法在-0.9 V~0.6 V掃描6~24 圈數後，藉FTIR、酸鹼度計以及氣相層析儀，分析經過乙醇電氧化產生出來的乙醛、乙酸產物，探尋、歸納過渡金屬觸媒之乙醇電氧化反應趨勢。 乙醇氧化反應分為兩種產物路徑：(1)12個電子轉移的C1路徑(2)4個電子轉移的C2路徑。本研究主要針對乙醇氧化反應的C2路徑產物(乙醛及乙酸)做分析。由產物分析的結果可以得知，在低電位(-0.9 V~0.6 V)的條件下，Pt、Pd、Au與Ag四種金屬作為觸媒，對乙醇電氧化成乙醛及乙酸之過程，相較於其他金屬擁有較高的催化活性。根據本研究結果顯示，在4個電子轉移的C2路徑下，各金屬觸媒對乙醇電氧化的催化活性由高至低依序為：Pt > Au > Ag > Pd > Rh > Ir > Cu > Ni > Co。再以此實驗結果，比較乙醇氧化的CV峰電流以及C2路徑的產物活性，可以推得Au與Ag兩種觸媒主要採C2路徑；Rh及Ir觸媒則採C1路徑；而Pt和Pd觸媒則是介於C1到C2之間。In this study, ethanol oxidation reaction (EOR) by electrochemical method on a series of metal-based catalysts, including, Pt, Pd, Rh, Ir, Au, Ag, Cu, Co, and Ni have been systematically investigated in alkaline media. The electrocatalyst were prepared by the impregnation reduction method, as metals ions were reduced by NaBH4 and deposited on Vulcan XC-72.The fabricated sample powder were initially examined by XRD, SEM, EDS and TEM to confirm their microstructure, chemical composition and particle size and deposited on glassy carbon electrode for the electrochemical measurement. Transition metal-based catalysts were analyzed and classified by the electrochemical measurement, cyclic voltammetry (CV). Trends of ethanol oxidation reaction on transition-metal catalysts were examined by FTIR, pH meter and Gas Chromatography to investigate distributions of products including acetaldehyde and acetic acid. After CV scans from -0.9 to 0.6 V in 1M ethanol in alkaline (0.1M KOH(aq)) medium. EOR involve tow product routes : (1) C1 pathway of 12 electron transfer (2) C2 pathway of 4 electron transfer. This study focus on analysis of EOR of C2 pathway products(acetaldehyde and acetic acid). The result found that Pt, Pd, Au, Ag metal catalysts have higher activity of catalysis than others in low voltage from -0.9 to 0.6 V. The sequence from high to low activity of EOR in C2 pathway follows Pt > Au > Ag > Pd > Rh > Ir > Cu > Ni > Co. According to a comparison between peak current and C2 product activity of EOR, it is possible to determine that main product route are C2 pathway for Au and Ag metal catalyst, C1 pathway for Rh, Ir, and between C1 and C2 for Pt, Pd.