甲酸與乙酸在Ge(100)表面的吸附與熱分解反應

Adsorption and Thermal Decomposition of Formic Acid and Acetic Acid on Ge(100)

郝婷(Hao, Ting)

指導教授 ： 洪偉修

國立臺灣師範大學/理學院/化學系/碩士(2012年)

摘要

我們利用程溫脫附質譜(TPD)及X光光電子能譜(XPS)研究甲酸(HCOOH)及乙酸(CH3COOH)在鍺(100)表面的吸附及熱分解反應。
　　在105K時，曝露甲酸於鍺(100)表面，會同時產生未分解的甲酸分子、和斷氧氫鍵分解的甲酸鹽(單螯結構, monodentate)吸附於表面；依照曝露量多寡，在275K未分解的甲酸會脫附或分解，部份分解的甲酸鹽會再轉換成另一種最穩定的吸附態結構(雙螯結構, bidentate)；當溫度升至470K時表面進行兩個競爭反應，為分解的甲酸鹽脫附或轉換成雙螯吸附態；約525K雙螯吸附態也開始脫附或生成CO2離去。因此甲酸在鍺(100)表面熱分解的產物為HCOOH、CO2和H2。
　　為了更近一步了解當碳鏈變長對羧酸分子吸附於鍺(100)表面機制的影響，進而去探討乙酸分子的熱分解過程，並與甲酸比較。發現兩者在鍺(100)表面的熱分解反應機制與溫度相似，但乙酸的熱分解產物只有CH3COOH本身的再結合脫附。此篇論文是針對上述化合物在鍺(100)表面的反應機制加以探討。

關鍵字

甲酸 ； 乙酸 ； 吸附 ； 熱分解

並列摘要

The adsorption and thermal reactions of formic acid (HCOOH) and acetic acid (CH3COOH) on Ge(100) surface were studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The desorption products of thermal reactions were monitored by TPD and the reaction intermediates were identified with XPS using synchrotron radiation.
At 105 K, HCOOH molecules either adsorb molecularly or dissociate to form surface formate for all durations of exposure. Chemisorbed HCOOH desorbs intact or dissociates to form surface formate (monodentate formate) on annealing to 275 K, whereas a portion of surface formates further transfers into a more stable configuration (bidentate formate). On annealing to 470 K, surface formates ether recombine with surface H to evolve HCOOH or transfer into bidentate formate by reacting with Ge adatoms. Finally, the bidentate formates undergo recombinative desorption or decomposition to desorb CO2. The products for thermal reaction of formic acid on Ge(100) are HCOOH, CO2, and H2.
To understand the influence of longer carbon chain to the mechanism, we investigated the thermal reaction of acetic acid (CH3COOH) on Ge(100). Acetic acid undergoes thermal reaction with similar mechanisms as formic acid, but proceeds exclusively recombinative desorption rather than formation of the other products. The detailed mechanisms of thermal reactions on Ge(100) are studied and discussed in this dissertation.

並列關鍵字

formic acid ； acetic acid ； adsorption ； thermal decomposition

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