Acta Phys. -Chim. Sin. ›› 2011, Vol. 27 ›› Issue (07): 1567-1573.doi: 10.3866/PKU.WHXB20110627

• THERMODYNAMICS, KINETICS, AND STRUCTURAL CHEMISTRY • Previous Articles     Next Articles

Influence of Ni Chemical States on the Partial Oxidation Mechanism of Methane: An Energetics Analysis

XIA Wen-Sheng, CHANG Gang, HOU Yu-Hui, WENG Wei-Zheng, WAN Hui-Lin   

  1. State Key Laboratory of Physical Chemistry for Solid State Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, Fujian Province Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian Province, P. R. China
  • Received:2011-04-01 Revised:2011-04-11 Published:2011-06-28
  • Contact: XIA Wen-Sheng, WAN Hui-Lin E-mail:wsxia@xmu.edu.cn; hlwan@xmu.edu.cn
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21033006, 20923004), Natural Science Foundation of Fujian Province, China (2007J0168), and National Key Basic Research Program of China (973) (2010CB732303).

Abstract:

An energetics analysis of the possible elementary steps involved in the partial oxidation of methane (POM) over different chemical states of Ni was carried out using the unity bond index-quadratic exponential potential (UBI-QEP) method. The results show that the rate determining step for the partial oxidation mechanism of methane is related to the chemical state of the Ni. Over reduced Ni the rate determining step for CO formation is the association of surface CH3 species with surface O species. Over a partial positive charged Ni surface the rate determining step is that methane dissociates into the CHxO species with the assistance of oxygen. Over the reduced and partial positive charged Ni sites in coexistence, however, the rate determining step depends on the competition between the formation of surface CH3 species and the recombination of surface CH3 species with surface O species. This competition is related to the chemical states of the Ni sites. If the partial positive charged Ni sites are predominant on the surface, the recombination of surface C species with surface O species and the recombination of surface H atom species favor CO and H2 formation because of decreasing barriers. The surface CHx species does not dissociate easily and surface carbon deposition is significantly inhibited.

Key words: Partial oxidation of methane, Nickel, Chemical state, Rate determining step, Mechanism, Energetics

MSC2000: 

  • O641