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(英文)  

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

作　　者：马嘉璧[1,2] 吴晓楠[1,2] 赵艳霞[1,2] 何圣贵[1] 丁迅雷[1] 

机构地区：[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 [2]中国科学院研究生院,北京100049

出　　处：《物理化学学报》2010年第7期1761-1767,共7页Acta Physico-Chimica Sinica

基　　金：supported by the Hundred Talents Fund of Chinese Academy of Sciences;National Natural Science Foundation of China(20703048,20803083,20933008);Center for Molecular Sciences Foundation of Institute of Chemistry,Chinese Academy of Sciences(CMS-LX200902)~~

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: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.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 V2O6-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 V2O6-and V4O1-1 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 mechanism for the reaction between surface O-species and hydrocarbon molecules.

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 

分 类 号：O643[理学—物理化学]