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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:V2O6-和V4O1-1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.V2O6-和V4O1-1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.
In order to reveal the mechanism of related catalytic reactions at the molecular level, a great deal of research has been conducted on the reaction between transition metal oxide clusters and hydrocarbon molecules. Compared with the transition metal oxide cluster cations, the activity of anions on some hydrocarbons In this work, we generated vanadium oxygen cluster anions, VxOy-, by laser sputtering and generated clusters near the thermal collision with alkanes (C2H6 and C4H10) and olefins (C2H4 And C3H6) were reacted in a fast-flowing reaction tube and time-of-flight mass spectrometry was used to detect the cluster distribution before and after the reaction.In the reaction of VxOy with paraffins, the products V2O6H- and V4O11H- were generated; in the reaction with olefins (X = C2H4 or C3H6). The density functional theory calculations show that V2O6- and V4O1-1 can activate the CH bonds of alkanes (C2H6 and C4H10), and also can react with olefins (C2H4 and C3H6) ) To form a five-membered ring structure (-VOCCO-), and both the activation of CH bond and the cycloaddition reaction need to go through the energy barrier of reaction which can be overcome.The theoretical calculation is consistent with the experimental observation.V2O6 - And V4O1-1 cluster with Oxygen atom (O · or O-) bond characteristics, active O-species are often found in the surface of the vanadium oxygen catalyst, the study revealed at the molecular level, the mechanism of surface oxygen species and hydrocarbons reaction .