CAJ | 학술논문

采用密度泛函理论(DFT)计算了CH4在电中性(CeO2)m(m=1~3)团簇上的活化情况，并对其机理进行了探讨。计算结果表明，甲烷C—H键在团簇上的活化为亲核加成模式，电子由团簇流向甲烷C—H反键轨道，使甲烷C—H键削弱而得以活化，反应的过渡态为四中心结构。团簇的桥氧位活化甲烷C—H键的活性大于端氧位，而三重桥氧位的活性高于二重桥氧位。团簇中作用位点Ce和O原子的电荷布居与其活化甲烷C—H的能力密切相关。溶剂的存在不仅降低了甲烷C—H活化自由能垒，而且使与甲烷作用的团簇各位点的活性差异缩小。
채용밀도범함이론(DFT)계산료CH4재전중성(CeO2)m(m=1~3)단족상적활화정황，병대기궤리진행료탐토。계산결과표명，갑완C—H건재단족상적활화위친핵가성모식，전자유단족류향갑완C—H반건궤도，사갑완C—H건삭약이득이활화，반응적과도태위사중심결구。단족적교양위활화갑완C—H건적활성대우단양위，이삼중교양위적활성고우이중교양위。단족중작용위점Ce화O원자적전하포거여기활화갑완C—H적능력밀절상관。용제적존재불부강저료갑완C—H활화자유능루，이차사여갑완작용적단족각위점적활성차이축소。
Although the rare earth oxide CeO2-based nano-catalysts have exhibited good performances for the activation of C—H of methane at low temperatures, the nature of the active sites and the C—H activation mechanisms are not clear. In this work, we employed the density functional theory( DFT) method to investi-gate the activation of C—H of CH4 and its mechanism at the electroneutral clusters(CeO2)m(m=1—3). The results show that the activation of C—H of methane on the clusters obeys the nucleophilic addition modes with the tetra-center structured transition state, in which the electrons are transferred from the clusters to the anti-bonding orbital of CH4 , then weakening and activating the C—H of methane. The bridge oxygen sites of the clusters display the higher activity toward the C—H of methane than the terminal oxygen sites, and the three-fold bridge sites show the greater activity for C—H activation of methane than the two-fold bridge sites. The charge population of the involved Ce and O atoms in the clusters is closely correlated to their ability toward the C—H activation of methane. In addition, not only decreases the solvation of the clusters the energy barrier for C—H activation of methane, but also makes the activity difference between the active sites of the clusters for C—H activation of methane be smaller.