物理化学学报 >> 2011, Vol. 27 >> Issue (07): 1567-1573.doi: 10.3866/PKU.WHXB20110627

热力学，动力学和结构化学 上一篇    下一篇

Ni的化学态对甲烷部分氧化反应机理的影响: 能学分析

夏文生, 常刚, 侯玉慧, 翁维正, 万惠霖   

  1. 固体表面物理化学国家重点实验室, 醇醚酯清洁化工生产国家工程实验室, 福建省理论计算化学重点实验室,厦门大学化学化工学院, 福建 厦门 361005
  • 收稿日期:2011-04-01 修回日期:2011-04-11 发布日期:2011-06-28
  • 通讯作者: 夏文生, 万惠霖 E-mail:wsxia@xmu.edu.cn; hlwan@xmu.edu.cn
  • 基金资助:

    国家自然科学基金(21033006, 20923004), 福建省自然科学基金(2007J0168)及国家重点基础研究发展规划项目(973) (2010CB732303)资助

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).

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摘要：

采用键指数归一-平方势(UBI-QEP)法对不同化学态Ni上甲烷部分氧化反应中各可能基元步骤进行了能学计算研究. 结果表明, 反应的速度控制步骤与金属Ni的化学态有关. 还原态Ni上CO形成的反应速度控制步骤为表面上CH3与O物种间的缔合, 而带部分正电荷的Ni上CO形成的反应速度控制步骤则为甲烷氧助解离形成表面CHxO物种. 还原态和带部分正电荷的Ni中心在表面上共存时, 反应的速度控制步骤将取决于表面CH3形成与表面CH3、O物种缔合两反应间的竞争, 其竞争的强弱涉及Ni的化学态. 此外, 反应活性中心向正电荷的Ni转化时, 会导致表面C和O及H和H物种缔合的活化能显著降低, 有利于CO、H2的形成, 而表面CHx物种解离则变得不容易, 表面积炭受到明显的抑制.

关键词: 甲烷部分氧化, 镍, 化学态, 速度控制步骤, 机理, 能量学

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