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研究生: 鍾國偉
論文名稱: 乙醇在Rh/Ce0.5Zr0.5O2(111)氧化金屬表面脫氫的可能反應機構
Computational Studies of Reaction Mechanisms of Dehydrogenation of Ethanol on the Rh/Ce0.5Zr0.5O2 (111) Surface
指導教授: 何嘉仁
學位類別: 碩士
Master
系所名稱: 化學系
Department of Chemistry
論文出版年: 2007
畢業學年度: 95
語文別: 中文
論文頁數: 71
中文關鍵詞: 乙醇脫氫化學含氧量
論文種類: 學術論文
相關次數: 點閱:175下載:2
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  • 中文摘要
    隨著化石燃料的日漸枯竭,人們正在找尋可以替代石油的能源來源。而氫氣(H2)是目前較佳的的料燃之一,將氫氣使用於內燃機引擎中,其燃燒產生的物質對環境是沒有污染性的。此外,氫氣也可以應用於H2/O2燃料電池的高效率發電方面,且具有相當的實用價值。乙醇是氫氣主要的來源之一,乙醇在合適的氧化物表面上時,加以合適的溫度,可以有絕佳的催化效果,而產生高效率的脫氫反應。在本文中,我們利用週期性的電子密度泛函理論的計算方法,探討乙醇在Rh/Ce0.5Zr0.5O2(111)表面上之可能的分解反應機構。結果發現,乙醇若以該分子的氧端吸附在Rh/CeO2(111)表極面的Ce上,比起其他表面原子而言(例如Rh與O原子),將有著較高的吸附能。是故乙醇首先將會以該氧端吸附在Rh/CeO2(111)表面的Ce上,而形成
    CH3CH2O(H)–Ce(a),再藉由接續的脫氫反應(斷去O–H以及H2C–H)
    ,之後形成一個穩定環狀的中間物Rh–CH2CH2–Ce(a) (oxametallacycle)。再者,該中間物會先在α-碳上接連斷去兩個C–H鍵而形成吸附中間物Rh–CH2CO–Ce(a)。最後Rh–CH2CO–Ce(a)將藉由斷去C–C鍵結而形成Rh–CH2(a) + 4H(a) + CO(g)的產物,最後這些產物在高溫下再產生脫附反應,而形成CH4(g) + H2(g) + CO(g)。

    Abstract
    Hydrogen is considered a desirable fuel for several reasons, among which hydrogen is the least polluting fuel that one can use in an internal–combustion engine, and it can serve in a highly efficient hydrogen/oxygen fuel cell to produce electricity. As a result, we applied periodic density–functional theory (DFT) to investigate the dehydrogenation of ethanol on a Rh/Ce0.5Zr0.5O2(111) surface. Ethanol is calculated to have the greatest energy of adsorption when the oxygen atom of the molecule is adsorbed onto a Ce atom in the surface, relative to other surface atoms (Rh or O). Before forming an oxametallacyclic compound (Rh–CH2CH2O–Ce(a)), two hydrogen atoms from ethanol are first eliminated; the barriers for dissociation of the O-H and the β-carbon (CH2–H) hydrogens are calculated to be 15.2 and 26.9 kcal/mol, respectively. The dehydrogenation continues with loss of two hydrogens from the α-carbon, forming an intermediate species Rh–CH2CO–Ce(a), . Scission of the C–C bond occurs at this stage to form Rh–CH2(a) + 4H(a) + CO(g). At high temperatures, these adsorbates desorb to yield the final products CH4(g), H2(g) and CO(g).

    目 錄 中文摘要 iii 英文摘要 iv 第一章、前言 1 第二章、 計算方法 7 第三章、乙醇在1Rh/Ce0.5Zr0.5O2 (111)slab上的脫氫反應機構 §3-1 固溶體的模擬 8 §3-2 slab切面的選擇與模擬 9 §3-3 乙醇吸附在表面Ce原子與Zr原子反應的比較 12 §3-4 1Rh 吸附在Ce0.5Zr0.5O2 (111)表面的結構 18 §3-5 乙醇在1Rh/Ce0.5Zr0.5O2 (111)slab脫H原子的可能反應機 構 20 第四章、乙醇在4Rh/Ce0.5Zr0.5O2 (111)slab上的脫氫反應機構 §4-1. 4Rh 吸附在Ce0.5Zr0.5O2 (111)表面的結構…………………38 §4-2. 乙醇在4Rh/Ce0.5Zr0.5O2 (111)slab上的吸附……………….39 §4-3. 乙醇在4Rh/Ce0.5Zr0.5O2 (111)slab脫H原子的可能反應機 構……………………………………………………………………..42 §4-4. 4Rh/Ce0.5Zr0.5O2 (111)表面OSC的討論…………………….57 第五章、結論......................................................................................60 參考文獻..............................................................................................62 第六章、附錄(乙醇在CeO2(111) cluster model的計算)………….65 §6-1. 計算軟體與方法…………………………………………….65 §6-2. CeO2 cluster model的模擬…………………………………..66 §6-3. 乙醇在CeO2(111) cluster model的吸附能…………………67 §6-4. 乙醇在2Rh/CeO2(111) cluster model的吸附與O-H基的 解離………………………………………………………………….69

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