高等学校化学学报

高等学校化学学报 ›› 2009, Vol. 30 ›› Issue (11): 2252.

• 研究论文 • 上一篇    下一篇

Co-Pd催化剂上CH4/CO2合成乙酸反应中CO2与表面金属物种作用的密度泛函理论研究

章日光, 黄伟, 王宝俊   

  1. 太原理工大学煤科学与技术教育部和山西省重点实验室, 太原 030024
  • 收稿日期:2008-12-02 出版日期:2009-11-10 发布日期:2009-11-10
  • 通讯作者: 黄伟, 男, 博士, 教授, 博士生导师, 主要从事碳化学和多相催化研究. E-mail: huangwei@tyut.edu.cn
  • 基金资助:

    国家自然科学基金(批准号: 20471040, 20906066, 20776093)、国家“九七三”计划(批准号: 2005CB221204)、教育部重点基金(批准号: 207016)和教育部博士点基金(批准号: 20060112014)资助.

Density Functional Theory Study on Interaction of CO2 with Metal Surface Carbon Species in Synthesis of Acetic Acid from CH4/CO2 on Co-Pd Catalysts

ZHANG Ri-Guang, HUANG Wei*, WANG Bao-Jun   

  1. Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, Taiyuan University of Technolgy, Taiyuan 030024, China
  • Received:2008-12-02 Online:2009-11-10 Published:2009-11-10
  • Contact: HUANG Wei. E-mail: huangwei@tyut.edu.cn
  • Supported by:

    国家自然科学基金(批准号: 20471040, 20906066, 20776093)、国家“九七三”计划(批准号: 2005CB221204)、教育部重点基金(批准号: 207016)和教育部博士点基金(批准号: 20060112014)资助.

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摘要：

采用广义梯度近似(GGA)的密度泛函理论(DFT)(DFT-GGA)对Co-Pd催化剂上CH4/CO2两步法合成乙酸反应中CO2与金属表面物种M—H(M=Co,Pd)和Pd—CH3的插入反应机理进行了研究, 给出了CO2与M—H和Pd—CH3的插入反应机理. 计算结果表明, 在CO2与M—H和Pd—CH3相互作用的4个反应路径中, 反应以CO2与Co—H作用生成产物HCOO—Co为动力学优先路径, 但由于HCOO以双齿形式与金属Co结合, 其结合能较大, 导致HCOO在金属表面不易脱附, 故较难形成甲酸; 反应生成H3CCOO—Pd产物路径次之, H3CCOO和Pd之间结合能较小, H3CCOO容易脱附形成主产物乙酸; 生成H3COOC—Pd反应为动力学最不利路径, 故甲酸甲酯为动力学禁阻产物; 计算结果与实验结果吻合得很好.

关键词: 二氧化碳; 乙酸; 反应机理; Co; Pd; 密度泛函理论; 广义梯度近似

Abstract:

The insertion reactions of CO2 with M—H(M=Co, Pd) and Pd—CH3 were systematically investigated by the first-principle DFT-GGA calculations. The mechanisms of CO2 reacting with M—H and Pd—CH3 were obtained for the direct synthesis of acetic acid from CH4/CO2 by a two-step reaction sequence on Co—Pd catalysts. The calculation result showed that the pathway that CO2 inserts into Co—H bonds forming HCOO—Co was the most advantageous in dynamics for all four designed reaction paths. However, HCOO was linked with Co in bi-dentate form, whose binding energy was very large, so the desorption of HCOO hardly taken place and formic acid was little produced. Meanwhile, the pathway that CO2 inserts into Pd—CH3 bonds forming H3CCOO—Pd was secondly preferential pathway favored in dynamics. The binding energy between H3CCOO and Pd was small, and desorption of H3CCOO easily occurred, so the main product was acetic acid. While methyl formate was inhibited by dynamics. The calculated result was in accordance with the experimental facts.

Key words: Carbon dioxide; Acetic acid; Reaction mechanism; Cobalt; Palladium; Density functional theory; General gradient approtimationry(GGA)

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