Pd掺杂CeO2团簇活化甲烷C-H的密度泛函理论研究  

Density functional theory study on the C-H bond activation of methane by Pd doped CeO2 cluster

作　　者：李倩倩 陈蓉芳 夏文生[1] 万惠霖[1] LI Qianqian;CHEN Rongfang;XIA Wensheng;WAN Huilin(College of Chemistry and Chemical Engineering,Xiamen University,Xiamen 361005,China)

机构地区：[1]厦门大学化学化工学院,福建厦门361005

出　　处：《厦门大学学报（自然科学版）》2020年第4期465-474,共10页Journal of Xiamen University：Natural Science

基　　金：国家自然科学基金(21373169)。

摘　　要：采用密度泛函理论(DFT)计算了甲烷在Pd掺杂的CeO2团簇(PdCeO4^2-和PdCe2O6^2-)上的活化情况.计算结果表明:Pd掺杂使CeO2团簇活化甲烷的能力增强;单重态Pd掺杂CeO2团簇活化C—H的能力总体上强于三重态团簇,而且团簇的构型和自旋多重度对反应能垒的影响较大;单重态团簇活化甲烷时反应过渡态为Ce(Pd)、O、H、C四中心结构,遵循四中心加成机理,最优活性位是在六元环团簇PdCe2O6^2--A(S)的Pd—O(B2)位点,活化能垒仅为39.2 kJ/mol;而三重态团簇活化甲烷时遵循氢摘除机理,过渡态由C、O、H三原子构成.此外,电荷分布和前线轨道分析结果表明,Pd掺杂CeO2团簇活化甲烷时电子由团簇流向甲烷.The importance of the close interaction between Pd and CeO2 has been stressed for many oxidation reactions,while the nature of the active sites in Pd-CeO2 remains to be identified.In this work,the activation of C—H of methane and its mechanism at the PdCeO4^2-/PdCe2O6^2--X(S/T)clusters at the UB3LYP/SDD+TZVP level were investigated using the density functional theory(DFT)method.The results show that Pd doping enhances the ability of CeO2 to activate methane.Generally,the singlet clusters are superior to triplet clusters in activating C—H,and the configuration has a great influence on the reaction energy barriers.On the singlet clusters,the transition states consist of Ce(Pd),O,H,C atoms,following the four-center addition mechanism.The optimal energy barrier is 39.2 kJ/mol,which occurs on the Pd—O(B2)of PdCe2O6^2--A(S)cluster.The transition state of the triplet clusters is composed of C,O and H atoms,which is consistent with the hydrogen removal mechanism.What's more,the charge population and frontier orbit analysis indicate that electrons flow from the cluster to methane when the C—H of methane is activated on the PdCeO4^2-/PdCe2O6^2--X(S/T)clusters.

关 键 词：Pd-CeO2 甲烷 密度泛函理论 活化机理 

分 类 号：O643.32[理学—物理化学]