Li和Al掺杂的MgO(001)表面负载W_3O_9团簇的构型与电子结构

Configuration and Electronic Structure of W_3O_9 Clusters Supported on Li- and Al-Doped MgO(001) Surfaces

采用基于第一性原理的分子动力学和量子力学相结合的方法,对W3O9团簇在经Li和Al原子掺杂的MgO(001)表面的负载构型、稳定性以及体系的电子结构进行了系统研究.结果表明,当掺杂发生在表层时,杂质原子的类型对W3O9团簇的负载构型有显著影响.对于缺电子的Li掺杂,负载后W3O9团簇环状构型并不稳定,转化为链状结构;而Al原子的掺杂则使得MgO(001)表面电子富余,此时W3O9团簇存在平躺和垂直两种吸附方式,二者能量稳定性相近,其中前者存在同时与三个W原子成键的帽氧结构.当掺杂发生在次表层时,两种掺杂体系W3O9的负载构型相似,团簇仍保持环状结构并倾向于采用垂直方式沉积在表面上.与Li掺杂体系相比,富电子的Al掺杂可显著增强W3O9与MgO(001)表面之间的结合能力,负载后有较多电子从表面转移到团簇中特定的W原子上,这将对W3O9团簇的催化性能产生显著影响.

The configuration, stability, and electronic structure of W3O9 clusters deposited on Li-and Al-doped MgO（001） surfaces were investigated using first-principles molecular dynamic simulations combined with quantum mechanical calculations. The results indicated that when the doping was in the top layer of the MgO （001） surface, the type of dopant had a great influence on the configuration of the W3O9 clusters. In the presence of electron-deficient Li doping, the cyclic conformation of the gas-phase W3O9 clusters was not stable, and it changed to a chain-like structure. While the introduction of the Al dopant made the surface electron-rich, the W3O9 clusters preferred paral el and vertical arrangements, respectively;the stabilities of the two configurations were similar, except that in the former case the one terminal oxygen of the clusters became a capped oxygen via bonding with three W atoms. When the doping was present in the sublayer, the W3O9 clusters stil showed a cyclic conformation, and favored a vertical deposition model. In comparison with the Li-doping of the MgO（001） surface, the Al-doping significantly enhanced the interactions between the W3O9 and the MgO（001） surface, and more electrons were transferred from the substrate to certain W atoms, which would have significant effects on the catalytic performance of the W3O9 clusters.