高等学校化学学报

高等学校化学学报

• 研究论文 • 上一篇    下一篇

Nb+离子活化甲烷脱氢反应机理密度泛函(DFT)研究

李建辉, 夏文生, 万惠霖   

  1. 厦门大学化学化工学院化学系, 固体表面物理化学国家重点实验室, 厦门 361005
  • 收稿日期:2006-01-04 修回日期:1900-01-01 出版日期:2006-12-10 发布日期:2006-12-10
  • 通讯作者: 夏文生

DFT Studies on Dehydrogenation Mechanism of Methane Activated by Gas-phase Niobium Cations

LI Jian-Hui, XIA Wen-Sheng, WAN Hui-Lin   

  1. State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemsitry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
  • Received:2006-01-04 Revised:1900-01-01 Online:2006-12-10 Published:2006-12-10

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摘要： 通过DFT-UB3LYP方法, 计算了五重、三重和单重自旋态下的气相Nb+离子活化甲烷脱氢反应的能量变化, 并对其直接式和插入式反应机理进行了比较, 考察了自旋翻转对反应的影响. 结果表明, 插入式脱氢较直接式有利, CH4上的H转移到Nb+上形成的中间体HNbCH+3中, 多重度由五重降为三重, 反应活化能垒显著降低; HNbCH+3可经四中心过渡态转化为(H2)NbCH+2, 最后生成三重态的NbCH+2+H2. 速控步骤为(H2)NbCH+2的脱氢. 此外, 通过对V+, Nb+, Ta+活化甲烷的比较研究了三者活化甲烷的反应活性.

关键词: 密度泛函理论（DFT）, 甲烷, 脱氢, 铌

Abstract: Density functional calculations were employed to investigate the quintet, triplet and singlet energies of methane direct- or inserted- dehydrogenation by gas-phase Nb+ as well as the influence of spin-inversion on the reaction mechanism. The results indicate that the inserted-dehydrogenation mechanism is more favorable than the direct-dehydrogenation. The minimum energy reaction path is thought to be related to the spin flip from 2S+1＝5 to 3, which decreases the activation barrier of methane-dehydrogenation significantly. The formed intermediate HNbCH+3 is transformed into(H2)NbCH+2 via a four-centered transition state, and the final product is the triplet NbCH+2+H2. The rate determined step of reaction is the dehydrogenation of (H2)NbCH+2. In addition, the reactivities of gas-phase group V cations(V+, Nb+ and Ta+) towards the dehydrogenation of methane were also discussed.

Key words: DFT, Methane, Dehydrogenation, Nb

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