物理化学学报 >> 2010, Vol. 26 >> Issue (07): 1761-1767.doi: 10.3866/PKU.WHXB20100737

化学动力学和分子动态学 上一篇    下一篇

钒氧阴离子团簇与小分子碳氢化合物反应的实验和理论研究

马嘉璧, 吴晓楠, 赵艳霞, 何圣贵, 丁迅雷   

  1. 中国科学院化学研究所, 分子动态与稳态结构国家重点实验室, 北京 100190
    中国科学院研究生院, 北京 100049
  • 收稿日期:2010-03-24 修回日期:2010-05-25 发布日期:2010-07-02
  • 通讯作者: 何圣贵, 丁迅雷 E-mail:shengguihe@iccas.ac.cn; dingxl@iccas.ac.cn

Experimental and Theoretical Studies of the Reactions between Vanadium Oxide Cluster Anions and Small Hydrocarbon Molecules

MA Jia-Bi, WU Xiao-Nan, ZHAO Yan-Xia, HE Sheng-Gui, DING Xun-Lei   

  1. State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
    Graduate University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2010-03-24 Revised:2010-05-25 Published:2010-07-02
  • Contact: HE Sheng-Gui, DING Xun-Lei E-mail:shengguihe@iccas.ac.cn; dingxl@iccas.ac.cn

摘要:

为了在分子层次上揭示相关催化反应的机理, 人们对过渡金属氧化物团簇与碳氢化合物分子反应进行了大量研究. 相比于过渡金属氧化物团簇阳离子, 阴离子对一些碳氢化合物的活性弱得多, 因此研究还很少. 在本工作中, 我们通过激光溅射产生钒氧团簇阴离子VxOy, 产生的团簇在接近热碰撞条件下与烷烃(C2H6和C4H10)以及烯烃(C2H4和C3H6) 在一个快速流动反应管中进行反应, 飞行时间质谱用来检测反应前后的团簇分布. 在VxOy与烷烃的反应中, 生成了产物V2O6H-和V4O11H-; 在与烯烃的反应中, 产生了相应的吸附产物V4O11X-(X=C2H4或C3H6). 密度泛函理论计算表明: V2O-6和V4O-11可以活化烷烃(C2H6和C4H10)的C—H键, 也可以与烯烃(C2H4和C3H6)发生3+2环化加成反应形成一个五元环结构(-V-O-C-C-O-), C—H键活化与环加成反应都需经历可以克服的反应能垒. 理论计算与实验观测结果相符合. V2O-6和V4O-11团簇都具有氧原子自由基(O·或O-)的成键特征, 活性O-物种也经常出现在钒氧催化剂表面, 因而本研究在分子水平上, 揭示了表面活性氧物种与碳氢化合物反应的机理.

关键词: 密度泛函理论, 钒氧团簇, 飞行时间质谱, C—H键活化, 多相催化

Abstract:

Reactions between transition metal oxide clusters and hydrocarbon molecules were extensively studied to reveal the mechanisms of the related catalytic processes at a molecular level. Compared with transition metal oxide cluster cations, anions are usually much less reactive toward some hydrocarbon molecules and thus much less studied. In this work, vanadium oxide cluster anions (VxOy) were prepared by laser ablation and reacted with alkanes (C2H6 and C4H10) and alkenes (C2H4 and C3H6) in a fast flow reactor under near thermal collision conditions. A time of flight mass spectrometer was used to detect the cluster distribution before and after the reactions. Hydrogen atom-pickup products V2O6H- and V4O11H- were observed in the reactions of VxOy with alkanes while the association products V2O6X- and V4O11X- (X=C2H4 or C3H6) were produced in the cluster reactions with alkenes. Density functional theory calculations predict that V2O-6 reacts with C2H6 and C4H10 by C—H activation and with C2H4 and C3H6 by 3+2 cycloaddition to form a five-membered ring structure (-V-O-C-C-O-) with surmountable reaction barriers. This is in agreement with the experiments. Both the V2O-6 and V4O-11 clusters have the bonding characteristics of oxygen-centered radicals (O·or O-) and these were also identified over the surface of the vanadium oxide based catalysts. This study provides a molecular level mechanismfor the reaction between surface O- species and hydrocarbon molecules.

Key words: Density functional theory, Vanadiumoxide cluster, Time of flight mass spectrometry, C—H activation, Heterogeneous catalysis

MSC2000: 

  • O644