CAJ | 학술논문

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氧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V4O11-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V4O11-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.
위료재분자층차상게시상관최화반응적궤리,인문대과도금속양화물단족여탄양화합물분자반응진행료대량연구.상비우과도금속양화물단족양리자,음리자대일사탄경화합물적활성약득다,인차연구환흔소.재본공작중,아문통과격광천사산생범양단족음리자VxOy-,산생적단족재접근열팽당조건하여완경(C2H6화C4H10)이급희경(C2H4화C3H6)재일개쾌속류동반응관중진행반응,비행시간질보용래검측반응전후적단족분포.재VxOy-여완경적반응중,생성료산물V2O6H-화V4O11H-;재여희경적반응중,산생료상응적흡부산물V4O11X-(X=C2H4혹C3H6).밀도범함이론계산표명:V2O6-화V4O11-가이활화완경(C2H6화C4H10)적C-H건,야가이여희경(C2H4화C3H6)발생3+2배화가성반응형성일개오원배결구(-V-O-C-C-O-),C-H건활화여배가성반응도수경력가이극복적반응능루.이론계산여실험관측결과상부합.V2O6-화V4O11-단족도구유양원자자유기(O·혹O-)적성건특정,활성O-물충야경상출현재범양최화제표면,인이본연구재분자수평상,게시료표면활성양물충여탄경화합물반응적궤리.
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 VxOy- 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.