Adsorption and Thermal Reaction of Short-Chain Alcohols on Ge(100)

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• 作者：Tsung-Hsiang Lin ; Bo-Yu Lin ; Ting Hao ; Hsiu-Yun Chien ; Jeng-Han Wang ; Wei-Hsiu Hung
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：February 14, 2013
• 年：2013
• 卷：117
• 期：6
• 页码：2760-2768
• 全文大小：492K
• 年卷期：v.117,no.6(February 14, 2013)
• ISSN：1932-7455

文摘

The adsorption and thermal decomposition of alcohols (CH₃OH, C₂H₅OH, and C₄H₉OH) on Ge(100) were investigated with temperature-programmed desorption and X-ray photoelectron spectra. At 105 K, CH₃OH adsorbs both molecularly and dissociatively on Ge(100). Chemisorbed CH₃OH molecules dissociate to form surface CH₃O and hydrogen in a temperature range 150鈥?00 K. Surface CH₃O can dehydrogenate to yield CH₂O as two desorption features, which depend on coverage. At small coverage, surface CH₃O undergoes mainly 伪-hydrogen elimination to desorb CH₂O at 490 K. At large coverage, another desorption of CH₂O occurs predominantly at 525 K, which is initiated by a recombinative desorption of CH₃OH. A calculation with density functional theory at the B3LYP/6-311+G** level shows that the dissociation of the O鈥?/i>H bond has a much smaller barrier (<40 kJ/mol) than those for C鈥?/i>O bond cleavage (>150 kJ/mol). Desorption of CH₂O results from the moderate barriers (110 kJ/mol) for cleavage of the C鈥?/i>H bond of surface CH₃O and weak adsorption energy of CH₂O (鈭?6 kJ/mol). The recombination of surface CH₃O with H occurs at large coverage with an energy barrier 127鈥?40 kJ/mol. Similarly to CH₃OH, C₂H₅OH and C₄H₉OH undergo the mechanism of thermal reactions through formation of alkoxyl intermediates. The longer-chain alkoxyl decomposes to desorb aldehyde at lower temperature because the interaction of its alkoxyl chain with the surface is stronger. On annealing to 570 K, all alkoxyl groups are completely removed from the surface via dehydrogenation and recombination to desorb aldehyde and alcohol, respectively. At a large coverage, the longer-chain alkoxyl undergoes dehydrogenation to a larger extent than recombinative desorption.