Yao Xiao-Dan, Zhu Kong-Jie, Teng Bo-Tao, Yu Cao-Ming, Zhang Yun-Lei, Liu Ya, Fan Maohong, Wen Xiao-Dong
School of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
Department of Chemical & Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA.
Phys Chem Chem Phys. 2016 Nov 30;18(47):32494-32502. doi: 10.1039/c6cp05406d.
The effects of strong interactions between Ti and ceria on the structures of Ti/CeO(111) are systematically investigated by density functional theory calculation. To our best knowledge, the adsorption energy of a Ti atom at the hollow site of CeO is the highest value (-7.99 eV) reported in the literature compared with those of Au (-0.88--1.26 eV), Ag (-1.42 eV), Cu (-2.69 eV), Pd (-1.75 eV), Pt (-2.62 eV) and Sn (-3.68 eV). It is very interesting to find that Ti adatoms disperse at the hollow site of CeO(111) to form surface TiO species, instead of aggregating to form Ti metal clusters for the Ti-CeO interactions that are much stronger than those of Ti-Ti ones. Ti adatoms are completely oxidized to Ti ions if they are monatomically dispersed on the next near hollow sites of CeO(111) (xTi-NN-hollow); while Ti ions are observed when they locate at the near hollow sites (xTi-N-hollow). Due to the electronic repulsive effects among Ti ions, the adsorption energies of xTi-N-hollow are slightly weaker than those of xTi-NN-hollow. Simultaneously, the existence of unstable Ti ions on xTi-N-hollow also leads to the restructuring of xTi-N-hollow by surface O atoms of ceria transferring to the top of Ti ions, or oxidation by O adsorption and dissociation. Both processes improve the stability of the xTi/CeO system by Ti oxidation. Correspondingly, surface TiO-like species form. This work sheds light into the structures of metal/CeO catalysts with strong interactions between the metal and the ceria support.
通过密度泛函理论计算系统地研究了Ti与二氧化铈之间的强相互作用对Ti/CeO(111)结构的影响。据我们所知，与Au（-0.88--1.26 eV）、Ag（-1.42 eV）、Cu（-2.69 eV）、Pd（-1.75 eV）、Pt（-2.62 eV）和Sn（-3.68 eV）相比，Ti原子在CeO中空位处的吸附能是文献报道中的最高值（-7.99 eV）。有趣的是，发现Ti吸附原子分散在CeO(111)的空位处形成表面TiO物种，而不是聚集形成Ti金属簇，因为Ti-CeO相互作用比Ti-Ti相互作用强得多。如果Ti吸附原子单原子分散在CeO(111)的次近邻空位处（xTi-NN-空位），它们会完全氧化为Ti离子；而当它们位于近邻空位处（xTi-N-空位）时，则会观察到Ti离子。由于Ti离子之间的电子排斥作用，xTi-N-空位的吸附能略弱于xTi-NN-空位的吸附能。同时，xTi-N-空位上不稳定Ti离子的存在也导致xTi-N-空位通过二氧化铈表面O原子转移到Ti离子顶部进行重构，或通过O吸附和解离进行氧化。这两个过程都通过Ti氧化提高了xTi/CeO体系的稳定性。相应地，形成了表面TiO类物种。这项工作揭示了金属与二氧化铈载体之间具有强相互作用的金属/CeO催化剂的结构。
