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Chemical and electrochemical hydrogenation of CO2 to hydrocarbons on Cu single crystal surfaces: insights into the mechanism and selectivity from DFT calculations

机译：Cu 2晶体表面二氧化碳至烃的化学和电化学氢化：DFT计算中的机制和选择性见解

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摘要

Atomic level mechanistic insights into the chemical and electrochemical reduction of CO2 on the Cu(111) and Cu(100) surfaces are presented based on DFT-based thermodynamic and kinetic calculations. On Cu(111), COads is firstly formed by the dissociative hydrogenation of CO2, and CHOads and CH2Oads are the key intermediates towards the chemical and electrochemical reduction of CO2 into methanol and CH4. Despite being thermodynamically or kinetically favoured, it is likely that CH2OHads instead of CH3Oads is the intermediate for methanol and CH4 formation. Based on the activation barriers, CH2OHads intermediate either forms CH3OH by direct hydrogenation or forms CH2ads by hydrogenative dissociation, which may be a parallel path in the CO2 reduction mechanism on the Cu(111) surface. Finally, the CH2 intermediate leads to formation of the hydrocarbons. On Cu(100), CO2 reduction takes a different pathway in the early stages; CO is formed through the direct dissociation of CO2 rather than hydrogenative dissociation as on the Cu(111) surface due to stronger bonding of CO. Further reduction of CO also undergoes a different pathway, in which CO dimerization is more easy to achieve, whereas CO hydrogenation is difficult on the Cu(100) surface. This explains why C2H4 is formed more favorably on the Cu(100) surface and CH4 is predominantly produced on the Cu(111) surface under both chemical and electrochemical conditions. In addition, DFT results showed for the first time that the electrochemical reduction would be expected to be highly favored at potentials of interest by CO2 reduction compared with chemical reduction and that the carbon dioxide anion radical ((CO2-)-C-center dot) is involved in the initial stage of CO2 electroreduction. Simultaneously, the results also explain partly why CH3OH is formed in gas phase chemistry and only CH4 is observed in electrochemistry on copper surfaces. By analyzing the chemical and electrochemical reduction paths, important mechanistic information is deduced on the Cu single crystal surfaces. The study of CO2 reduction mechanisms on copper will lead to a deeper understanding of the reaction chemistry and could eventually lead to the design of more efficient and selective catalysts.
机译：基于基于DFT的热力学和动力学计算，给出了Cu（111）和Cu（100）表面上CO 2的化学和电化学还原的原子水平机械洞察。在Cu（111）上，首先通过二氧化碳的解离氢化形成CoAD，并且钢筋和CH2载是朝向甲醇和CH 4的CO 2的化学和电化学还原的关键中间体。尽管在热力学或动力学上受到青睐，但CH2OHAD可能代替CH 3载是甲醇和CH 4形成的中间体。基于活化屏障，CH2Ohads通过直接氢化或通过氢化解离形成CH 3 OH而中间体形成CH 3 OH，其可以是Cu（111）表面上的CO 2还原机制中的平行路径。最后，CH2中间体导致形成烃。在Cu（100）中，CO 2还原在早期阶段采用不同的途径;由于CO的粘合强度，通过CO 2的直接解离CO 2而不是致癌的CO 2而不是致癌的CO。进一步减少CO的还原也经历了不同的途径，其中CO二聚化更容易实现，而CO在Cu（100）表面上难以氢化。这就解释了为什么C2H4形成更有利地在Cu（100）表面和CH4是在Cu主要产生的化学和电化学条件下（111）表面。此外，DFT结果表明对于第一次电化学还原将预期高度由CO 2还原在感兴趣电位青睐与化学还原和相比二氧化碳阴离子自由基（（CO2 - ） - C-中心点）参与CO2电氧化的初始阶段。同时，结果还分别解释了为什么CH 3 OH在气相化学中形成，并且在铜表面的电化学中仅观察到CH 4。通过分析化学和电化学还原路径，在Cu单晶表面上推导出重要的机械信息。对铜二氧化碳减少机制的研究将导致对反应化学的更深入了解，最终可能导致更有效和选择性催化剂的设计。

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  • 来源
    《RSC Advances》 |2015年第71期|共11页
  • 作者

    Ou Lihui;

  • 作者单位

    Hunan Univ Arts &

    Sci Coll Chem &

    Chem Engn Changde 415000 Peoples R China;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 化学;
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