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論文名稱 Title |
硝基甲烷在銅(111)表面之熱化學研究 Thermal Chemistry of Nitromethane on Cu(111) |
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系所名稱 Department |
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畢業學年期 Year, semester |
語文別 Language |
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學位類別 Degree |
頁數 Number of pages |
59 |
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研究生 Author |
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指導教授 Advisor |
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召集委員 Convenor |
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口試委員 Advisory Committee |
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口試日期 Date of Exam |
2012-07-26 |
繳交日期 Date of Submission |
2012-07-31 |
關鍵字 Keywords |
異構化、亞硝基甲酯、硝基甲烷、銅(111)、超高真空系統 UHV, Cu(111), TPD, RAIRS, nitromethane, methyl nitrite, isomerization |
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統計 Statistics |
本論文已被瀏覽 5656 次,被下載 950 次 The thesis/dissertation has been browsed 5656 times, has been downloaded 950 times. |
中文摘要 |
在化學製程中,碳氮化合物與金屬的催化作用為一重要課題。硝基烷類是一 種具有高爆炸性的物質,其中硝基甲烷是一個簡單且備受關注的硝基化合物。在 許多氣相研究的報導中指出硝基甲烷可經由多個反應通道,有機會進行異構化反 應轉換成亞硝基甲酯,關鍵在於nitro-nitrite 能障為55.5 kcal/mol 且CH3O-NO 鍵 能僅有42 kcal/mol 與硝基甲烷C-N 鍵(鍵能60.1 kcal/mol)的斷裂互為競爭反應。 本實驗於超高真空系統中進行,在100 K 將硝基甲烷吸附在Cu(111)表面,藉 由程溫脫附質譜(TPD)和表面反射式紅外光譜技術,觀測分子中,C-N,N-O 與C-O 鍵的變化。TPD 偵測結果顯示,在160 K 和183 K,分別為硝基甲烷多層與單層分 子脫附;278 K 有NO 的生成脫附, 推測硝基甲烷發生了異構化反應 (CH3NO2«CH3ONO)形成亞硝基甲酯,隨升溫造成O-N 鍵斷裂,使NO 由Cu(111) 表面脫附;314 K 有CO 脫附;於更高溫367 K,則出現H2、H2O 和CH4 等產物脫附。 輔以同位素氘取代硝基甲烷(CD3NO2)實驗佐證出H2(D2)、H2O(D2O)及CH4(CD4) 的脫附確實來自於起始物硝基甲烷與Cu(111)單晶表面的作用;455 K 觀察到CO2 脫附。未發生異構化之硝基甲烷,C-H 鍵和O-N 鍵的斷裂在表面留下CN group, 363 K 形成HCN 脫附;在815 K 則形成二聚體C2N2 脫附。由RAIS 光譜可知低溫 100 K 硝基甲烷確實吸附於Cu(111)表面上,170 K 生成methoxy(CH3O)與 formyl(HCO)吸附於銅(111)表面。在250 K 指認1535 cm-1 為氮氧鍵的伸縮振動 n(NO); 270 K 分別以side-bonded CN(ad)及aminomethylene(HC-NH2)吸附於表面; 330 K 指認2173 cm-1 為terminal-CN(ad)的伸縮振動n(CN),此特徵峰直到900 K 才 消失與TPD 中C2N2(m/z 52)於815 K 脫附實驗吻合。 |
Abstract |
Nitromethane is the simplest organic-nitro compound as well as the archetype of an important class of high explosive. Homogeneous nitromethane reactions have been the subject of extensive studies. Particularly the unimolecular isomerization of nitromethane to methyl nitrite is proven to be competitive with simple C-N bond (bond energy 60 kcal/mol) rupture. The activation energy for the rearrangement was measured to be 55.5 kcal/mol and methyl nitrite has a very weak CH3O-NO bond energy 42 kcal/mol lower than that for homolysis. The thermal chemistry of nitromethane on Cu(111) was studied by a combination of temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) techniques. TPD spectra show that the desorption features include the physisorbed multilayer and monolayer of CH3NO2 at 150 and 190 K, respectively. The major decomposition pathway is via cleavage of O-N bond to yield a major product NO, which is characterized by m/z 30(NO+). A possible contribution from isomerization of nitromethane to methyl nitrite (CH3NO2 CH3ONO) on the surface cannot be ruled out at 278 K. In addition to isomerization, the dehydrogenation products CO and CO2 are also unveiled as part of the desorption features at 314 and 455 K, respectively. We can further prove the reactivity of nitromethane on Cu(111) at 367 K by using the deuterated form of nitromethane which reveals the corresponding desorption TPR/D signals of D2, D2O and CD4. However, we find that nitromethane also reacts by dissociating the C-H bond and the O-N bond, however, leaving the C-N bond intact. Along this reaction channel, HCN desorbs as a product above 360 K, as evidenced by a broad desorption feature of m/z 27. Dimerization of CN to C2N2 occurs at 815 K. The RAIR spectroscopy demonstrates that nitromethane is indeed adsorbed on Cu(111) at 100 K. The formation of methoxy and formyl are supported by the observation of desorption of NO at 278 K with the characteristic NO stretching mode found at 1535 cm-1. Moreover, we assign side-bonded CN and aminomethylene (HC-NH2) present on Cu(111). After the surface is annealed to 330 K, a signature band at 2173 cm-1 is assigned to terminal-bounded CN stretching mode. This band eventually fades out above 900 K consistent with the evolution of cyanogen at 815 K. |
目次 Table of Contents |
第壹章 緒論 1 第貳章 實驗設備 6 2.1 儀器裝置 6 2.2 實驗藥品 7 第參章 實驗結果 8 3.1 硝基甲烷在Cu(111)表面上的熱化學反應 — 程序控溫反應/脫附實驗 8 3.2 反射式吸收紅外光譜實驗 16 3.2.1 CH3NO2在Cu(111)表面之RAIR光譜 17 3.2.2 Methyl Nitrite 的證據 — Methoxy與Formyl中間體的形成(170 ~ 210 K) 20 3.2.3 Methyl Nitrite(CH3O-NO)於表面生成之另一證據: O-N鍵的斷裂導致一氧化氮的吸附(210 ~ 250 K) 21 3.2.4 Side-Bonded CN(ad) 及Aminomethylene HC-NH2於表面生成(250 ~ 270 K) 23 3.2.5 Terminal-CN(ad) Groups於表面生成 25 第肆章 討論 28 4.1 硝基甲烷(CH3NO2)進行異構反應轉換成亞硝基甲酯(CH3ONO) 28 4.1.1 Nitro-Nitrite異構化的發生 28 4.1.2 亞硝基甲酯的反應 30 4.1.3亞硝基甲酯在不同金屬表面之研究 33 4.2 硝基甲烷在Cu(111)上的熱化學反應 34 4.3 硝基甲烷在Cu(111)及不同金屬表面之研究 37 4.3.1 硝基甲烷在不同表面的熱化學反應 37 4.3.2 硝基甲烷在不同表面的鍵結模式 39 4.4 計算部分 41 第伍章 結論 43 第陸章 參考文獻 44 |
參考文獻 References |
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