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    题名: DFT study of the formation of CH2=CF2 through both methylene insertion and b-fluoride elimination on the Ag(111) surface
    作者: 林志興;Lin, Jyh-shing;Chou, Wen-Chi
    贡献者: 淡江大學化學學系
    关键词: Fischer–Tropsch process;Ag(111) surface;ultrasoft pseudopotential;density functional theory;temperature-programmed reaction;generalized gradient spin-polarized approximation
    日期: 2004-04-01
    上传时间: 2009-12-01
    出版者: World Scientific Publishing
    摘要: Total energy calculations based on (1) density functional theory (DFT) in connection with ultrasoft pseudopotential and generalized gradient spin-polarized approximation (GGSA) and (2) the partial structural constraint path minimization (PSCPM) method have been used to investigate the energetically more favorable pathway for methylene (CH2) insertion into the Ag–CF3 bond followed by β-fluoride elimination to generate an isolated CH2=CF2(g) above the Ag(111) surface. The diffusion of the fcc-hollow site of CF3(ads) toward the bridge site of CH2(ads) is proposed as an energe*tically more favorable path for CH2 insertion into the Ag–CF3 bond to form the bridge site of CH2CF3(ads) on the Ag(111) surface. Then we proceed with β-fluoride elimination to form an isolated CH2=CF2(g) and the bridge site of F(ads) on the Ag(111) surface. Our calculated energy barrier for β-fluoride elimination is 0.715 eV higher than that for CH2 insertion on the Ag(111) surface. These calculated results imply that β-fluoride elimination rather than CH2 insertion on the Ag(111) surface controls the CH2=CF2(g) formation rate as observed from temperature-programmed reaction (TPR) experimental data. Finally, we attribute these different energy barriers to the different transition state structures — largely distorted seven-centered versus less distorted four-centered — involved in these two different processes.
    關聯: Surface review and letter11(2), pp.229-234
    DOI: 10.1142/S0218625X04006128
    显示于类别:[化學學系暨研究所] 期刊論文

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