Chem. J. Chinese Universities ›› 2021, Vol. 42 ›› Issue (9): 2878.doi: 10.7503/cjcu20210282

• Physical Chemistry • Previous Articles     Next Articles

Theoretical Study on Direct Conversion of CH4 and CO2 into Acetic Acid over MCu2Ox(M = Cu2+, Ce4+, Zr4+) Clusters

ZHONG Shengguang, XIA Wensheng(), ZHANG Qinghong, WAN Huilin   

  1. State Key Laboratory of Physical Chemistry of Solid State Surface,National Engineering Laboratory for Green Chemical Productions of Alcohols?Ethers?Esters,Key Laboratory of Theoretical and Computational Chemistry of Fujian Province,College of Chemistry and Chemical Engineering,Xiamen University,Xiamen 361005,China
  • Received:2021-04-25 Online:2021-09-10 Published:2021-09-08
  • Contact: XIA Wensheng E-mail:wsxia@xmu.edu.cn
  • Supported by:
    the National Key R&D Program, China(2019YFE04400);the National Natural Science Foundation of China(21373169);the Program for Innovative Research Team in University of Ministry of Education, China(IRT1036)

Abstract:

Transformation and utilization of methane and carbon dioxide are important to chemical industry of natural(shale) gas and environmental protection. The properties of electroneutral clusters MCu2Ox(M=Cu2+, Ce4+, Zr4+x=3, 4) and their influences on direct conversion of methane and carbon dioxide to acetic acid were investigated by means of density functional theory(DFT). The clusters-catalyzed reaction consists of C—H activation of methane, C-C coupling by carbon dioxide insertion, CH3COO rotation, hydrogen transfer. The first 2 steps are essential to the proceeding of the whole reaction, in which C—H and C-C interacted with the active sites of the clusters, respectively, leading to the formation of 4-centered transition states. During this process, electrons transferred to the clusters from methane, and then transferred to carbon dioxide, which activated both C—H bond of CH4 and C=O bond of CO2, and then drove C-C coupling. With introducing of Ce or Zr, the clusters displayed the structure not only with 6-membered ring(I), but also double 4-membered ring with Ce or Zr located in the center(II) or end(III). The structures and electron spin states of the clusters are associated with the reactivity. It was found that the clusters with low spin states preferred to C—H activation, and the ones with high spin states tended to C-C coupling. Among the doped clusters with three types of structures, the cluster III at triplet state well matches C—H activation with C-C coupling in the targeted reaction. Comparing the clusters with/without doping for the same structure and electron spin state, the local charge at active sites was changed with the doping of Ce or Zr into copper oxide clusters. This weakened slightly the ability of the clusters in activating C—H bond of methane, but decreased significantly Gibbs free barrier for C-C coupling, and then drove well the overall reaction. The doped Zr showed better promoting roles than Ce in this process.

Key words: Modified copper oxide, Methane, Carbon dioxide, Acetic acid, Density functional theory

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