English  |  正體中文  |  简体中文  |  全文笔数/总笔数 : 50122/85141 (59%)
造访人次 : 7884020      在线人数 : 34
RC Version 7.0 © Powered By DSPACE, MIT. Enhanced by NTU Library & TKU Library IR team.
搜寻范围 查询小技巧:
  • 您可在西文检索词汇前后加上"双引号",以获取较精准的检索结果
  • 若欲以作者姓名搜寻,建议至进阶搜寻限定作者字段,可获得较完整数据
  • 进阶搜寻

    jsp.display-item.identifier=請使用永久網址來引用或連結此文件: http://tkuir.lib.tku.edu.tw:8080/dspace/handle/987654321/25175

    题名: Reaction Mechanism of N2/H2 Conversion to NH3: A Theoretical Study
    作者: 黃德彥;Hwang, Der-yan;Mebel, Alexander M.
    贡献者: 淡江大學化學學系
    日期: 2003-04-24
    上传时间: 2009-12-01
    出版者: American Chemical Society (ACS)
    摘要: Ab initio G2M(MP2)//MP2/6-31G** calculations have been performed to study the molecular and radical chain reaction mechanisms of nitrogen hydrogenation through sequential additions of three H2 molecules to N2 producing NH3 + NH3. All reaction steps of the molecular mechanism are shown to be slow owing to high barriers for the molecular hydrogen additions. The three-center 1,1-H2 additions are significantly more preferable as compared to the four-center 1,2-additions. The most favorable reaction pathway involves the steps N2 + H2 → TS1a → NNH2, NNH2 + H2 → TS3a → H2NNH2, H2NNH2 → TS4 → HNNH3, and HNNH3 + H2 → TS5 → NH3 + NH3, with the barriers calculated as 125.2, 30.7, 60.5, and 24.6 kcal/mol, respectively. The addition of the first molecular hydrogen is thus the rate-determining stage of nitrogen hydrogenation. The formation of hydrazine can be facilitated by a spontaneous reaction of two cis-HNNH molecules by the dihydrogen transfer mechanism. The radical chain mechanism includes the N2 + H → N2H, N2H + H2 → HNNH + H, HNNH + H → N2H3, N2H3 + H2 → H2NNH2 + H, H2NNH2 + H → NH2 + NH3, and NH2 + H2 → NH3 + H sequential reactions with the barriers of 17.1, 41.6, 6.4, 29.1, 10.7, and 10.6 kcal/mol, respectively. Nitrogen hydrogenation can be catalyzed by H atoms with the barrier for the slowest reaction step decreasing from 125 to 42 kcal/mol. The reaction of two NH(3Σ-) radicals is predicted to be fast and to form N2 + H2 with high exothermicity. The reaction of two NH2 radicals can produce NNH2 + H2 with exothermicity of 19.8 kcal/mol and a barrier of 10.9 kcal/mol relative to the reactants, or NH3 + NH(3Σ-), through a barrierless, 14.3 kcal/mol exothermic, but spin-forbidden channel. We also report rate constants and equilibrium constants for all considered reactions calculated using the transition state theory and ab initio energies and molecular parameters, which can be employed for kinetic modeling of chemical processes involving nitrogen- and hydrogen-containing substances.
    關聯: Journal of physical chemistry A 107(16), pp.2865-2874
    DOI: 10.1021/jp0270349
    显示于类别:[化學學系暨研究所] 期刊論文


    档案 描述 大小格式浏览次数



    DSpace Software Copyright © 2002-2004  MIT &  Hewlett-Packard  /   Enhanced by   NTU Library & TKU Library IR teams. Copyright ©   - 回馈