Acta Physico-Chimica Sinica ›› 2019, Vol. 35 ›› Issue (9): 1005-1013.doi: 10.3866/PKU.WHXB201809006

Special Issue: 碳氢键活化

• Article • Previous Articles     Next Articles

Methane Activation on (Au/Ag)1-Doped Vanadium Oxide Clusters

Dan WANG1,Xunlei DING2,*(),Henglu LIAO2,Jiayu DAI1,*()   

  1. 1 Department of Physics, College of Arts and Sciences, National University of Defense Technology, Changsha 410073, P. R. China
    2 School of Mathematics and Physics, North China Electric Power University, Beijing 102206, P. R. China
  • Received:2018-09-04 Accepted:2018-10-15 Published:2018-10-18
  • Contact: Xunlei DING,Jiayu DAI E-mail:dingxl@ncepu.edu.cn;jydai@nudt.edu.cn
  • Supported by:
    The project was supported by the National Natural Science Foundation of China(91545122);The project was supported by the National Natural Science Foundation of China(11774429);the Science and Technology Project of Hunan Province, China(2017RS3038);the Fundamental Research Funds for the Central Universities, China(JB2015RCY03)

Abstract:

The activation of methane (CH4) is a key step in its conversion to more valuable products. The activation mechanisms of CH4 on catalyst surfaces have been widely studied using gas-phase cluster models, which can be operated on systems with a precise number of atoms and determined structures. Herein, we have used MV3Oyq (M = Au/Ag, y = 6–8, q = 0 or ±1) clusters, in which a single Au or Ag atom was supported on vanadium oxide clusters, as simple models to mimic the properties of newly developed single-atom catalysts. The adsorption and activation of CH4 on these MV3Oyq clusters were systematically studied via density functional theory calculations at the B3LYP/Def2-TZVP level, which provided insights into the geometric structures, adsorption energies, and charge distributions of the adsorption systems. Five Au-containing clusters, AuV3O6, AuV3O7, AuV3O8, AuV3O6+, and AuV3O7+, were able to activate CH4, while other clusters, including all Ag-containing clusters, were inert. In the active clusters, all Au atoms were adsorbed on the O-atom sites of the supporting V3Oyq cluster and served as the active sites for CH4 activation. The activation of CH4 was characterized by the lengthened C―H bond (approximately 115 pm), short distances between CH4 and Au (approximately 184 pm), relatively high adsorption energies of CH4 (~0.590–1.145 eV), and significant electron transfer from CH4 to the clusters (above 0.08e). In particular, AuV3O8, which is a neutral cluster with a close-shell electronic state, can activate CH4 with a C―H bond length of 115 pm, Au―H bond length of 183 pm, the adsorption energy of CH4 of 0.853 eV, and the charge on CH4 of +0.088e. The charge state of the cluster has a significant effect on the activation ability: cationic clusters are the most active, followed by neutral clusters, while anionic clusters have the lowest activities toward CH4. Consistently, the local charge on the M atom has a positive correction with the activation ability of MV3Oyq clusters with a certain M. However, as compared to Au-containing clusters, Ag-containing clusters have lower activities despite the higher local charges on Ag in each MV3Oyq cluster. The results indicate that the inclusion of D3 dispersion correction has a small effect on structures and energies. This study may serve as a foundation for further research on the activation of CH4 on single-atom catalysts and provides useful information on rational designing of single-atom catalysts for CH4 conversion at low temperatures.

Key words: Methane activation, Metal oxide clusters, Noble metal, Single-atom catalysis, Density functional theory

MSC2000: 

  • O641