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研究生: 鄭孟勤
Cheng, Meng-Chin
論文名稱: 以第一原理計算探討銠金合金表面對甲醇反應的效果及反應路徑的影響
The mechanism investigation of methanol reaction on Rh-Au alloy by first principles calculation
指導教授: 王禎翰
Wang, Jeng-Han
學位類別: 碩士
Master
系所名稱: 化學系
Department of Chemistry
論文出版年: 2018
畢業學年度: 106
語文別: 中文
論文頁數: 56
中文關鍵詞: 甲醇氧化還原密度泛函理論計算RhAu合金
英文關鍵詞: methanol oxidation reaction, density functional theory calculation, RhAu alloy
DOI URL: http://doi.org/10.6345/THE.NTNU.DC.009.2018.B05
論文種類: 學術論文
相關次數: 點閱:104下載:11
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  • 本文運用密度泛函理論計算在RhAu合金催化表面,甲醇氧化反應的反應機構。RhAu是在將Rh原子層建構在Au(100)表面,其原子半徑差距會使Rh層在表面扭曲,低配位的Rh原子將形成類似團簇(cluster)的結構。相較於其在Rh(100)純金屬表面上的結果,會有更佳的反應活性。因此將從扭曲表面形成物理結構上的差別,以及Rh與輔層的Au接觸產生電子層面的影響,兩方面討論RhAu 表面能有效進行MOR的原因。RhAu表面的Rh電子分布更集中,強化其吸附能力並降低了O-H斷鍵的反應能障,影響了較重要的兩項反應途徑(CH3OHCH3OCH2O)。
    此外,我們利用類似構型的Rh2Au36、Rh2Au38、Rh36Au2、Rh38Au2團簇,分析電子層面對於反應能力的影響。其中Rh2Au38有更多的輔層Au原子並表現出較RhAu表面更強的反應能力。DOS(density of state)的結果顯示RhAu表面的Rh會有較高密度的電子形成鍵結,強化吸附能力並帶來更佳的反應活性。計算結果與實驗觀察到,少量Rh添加於Au表面,甲醇反應活性將會急遽增強,而增強幅度將隨Rh比例上升而趨帄緩。
    最後我們Rh(100)表面吸附O及OH,討論甲醇在氧的輔助下的斷鍵能力,並與乾淨Rh(100)的結果比較。與氧相較,羥基在表面的輔助斷鍵的表現較弱。

    First principles calculations have been used to investigate the mechanism of methanol reaction on bimetallic RhAu catalysts. We initially compare the reactions on RhAu and Rh(100) surfaces. RhAu surface was built by adding a Rh layer on Au(100) to simulate the Rh deposition on Au substrate in the experiment; the Rh layer shrunk forming the low-coordinate surface Rh atoms. The higher active of methanol reaction on RhAu surface, thus, corresponds to both the physical effect from the shrunk Rh layer and the electronic effect caused by the subsurface Au atoms. Surface Rh atoms of RhAu surface has more localized charge distribution due to the low coordination and accumulate more charge form subsurface Au atoms that can strengthen the methanol adsorption and lower the dissociation barrier for initial O-H bond cleavage, the two key steps that control the activity of methanol reaction. Furthermore, we examined RhAu clusters of Rh2Au36, Rh2Au38, Rh36Au2 and Rh38Au2 with similar shapes to analyze electronic effect contributed to reaction activity. Rh2Au38 with more substrate Au elements shows the highest activity, better than that on RhAu surface. The detailed electronic structures of those RhAu bimetals have also been examined by the density of state analysis. The computational results have been confirmed from the experimental observation that the activity increases dramatically as small amount of Rh deposited on Au substrate; the activity becomes saturated as the deposited Rh increases. Finally, we introduce surface oxygen and hydroxyl neighboring to the methanol and its fragment to investigate the oxidation assisted methanol reaction on Rh(100). Surface hydroxyl moderately enhanced the MOR while surface oxygen shows small assistance.

    第一章 緒論 8 1-1 前言 8 1-2 燃料電池應用甲醇反應 9 1-3 甲醇氧化反應 10 1-4 金屬電極催化助益 10 1-5 研究動機 14 第二章 理論計算原理 15 2-1 密度泛函理論介紹 15 2-1-1 Kohn-Sham Equation 15 2-1-2 交換關聯函數 16 2-1-3 自洽過程 17 2-1-4 基底 17 2-1-5 布洛赫定理(Broch theorem) 17 2-1-6 虛位勢(Pseudopotential) 18 2-2 系統與軟體 18 第三章 結果與討論 20 3-1 MOR在Rh(100)及RhAu合金表面計算 20 3-1-1 Rh(100)及RhAu表面模型建立 20 3-1-2 MOR於Rh(100)表面之反應途徑 21 3-1-3 比較Rh(100)與RhAu吸附能力 26 3-1-4 RhAu合金表面DOS分析 28 3-1-5 分析Rh(100) 及RhAu反應途徑 30 3-1-6 實驗產物推測反應路徑 33 3-2 MOR在Rh&Au 團簇計算 36 3-2-1 團簇模型建立 36 3-2-2 團簇吸附表現 37 3-2-3 團簇反應能力分析 41 3-2-4 比較RhAu團簇表現與實驗結果 43 3-2-5 RhAu團簇與合金表面結果比較 44 3-3 吸附氧參與MOR之Rh(100)表面 46 3-3-1 共吸附穩定度 46 3-3-2 O及OH共吸附下MOR表現 47 第四章 結論 49 第五章 附錄 50 5-1 計算參數檔案 50 第六章 參考資料 54

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