Hydrocarbon chain growth and hydrogenation on V(100): a density functional theory study
Hydrocarbon chain growth and hydrogenation on V(100): a density functional theory study
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DOI：
10.1039/c4ra15368e
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发表时间：
2015
期刊：
影响因子：
3.9
通讯作者：
Hui Wang;Jing-yao Liu;Z. Chai;Dongqi Wang
中科院分区：
文献类型：
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作者：
Hui Wang;Jing-yao Liu;Z. Chai;Dongqi Wang
用周期密度泛函理论(DFT)方法研究了V(100)上CO的活化、CHX(x=0-4)和C2Hy(y=0-5)物种的加氢以及碳链的扩展。结果表明，CO在V(100)面上的活化是通过直接解离而不是H辅助途径进行的。CHX/C2Hy的加氢反应(CC除外)和C-C耦合基元步骤在热力学和动力学上都是不利的。前者的反应能垒比后者的低。反应物的高覆盖率和熵效应可能是导致加氢和碳链扩展的主要因素。根据上述结果建立的简单微观动力学模型表明，在300-800K的温度范围内，CH2是表面上的主要CHX物种，CH2是C链的组成单元CH2的高覆盖率，CH2CH2通过偶联反应形成CH2CH2，然后从表面解吸。CH2CH主要由CH2+CH偶联，CH2插入生成CH2CHCH3形成。虽然考虑到能垒，CH比CH2更有可能对链传播负责，但在所考虑的条件下，它的贡献受到其低覆盖率的影响。这些结果与实验结果吻合较好。
The activation of CO, hydrogenation of CHx (x = 0–4) and C2Hy (y = 0–5) species and carbon chain propagation on V(100) were studied by means of periodic density functional theory (DFT) calculations. The results indicate that the activation of CO is very facile on V(100) via direct dissociation rather than H-assisted pathways. The hydrogenation of CHx/C2Hy (except for CC) and the C–C coupling elementary steps are thermodynamically and kinetically unfavorable. The energy barriers to the former reactions are lower than those to the latter ones. The high coverage of reactants and the entropic effect may be the dominant factors responsible for the hydrogenation and carbon chain propagation. The simple microkinetic model built on the basis of the above results shows that CH2 is the dominant CHx species on the surface in the temperature range of 300–800 K. Starting from a high coverage of CH2, the building block of the C-chain, CH2CH2 forms via a coupling reaction and then desorbs from the surface. CH2CH, appearing as the precursor, mainly forms from the coupling of CH2 + CH followed by CH2 insertion leading to CH2CHCH3. Although CH is more likely responsible for the chain propagation than CH2 in view of energy barriers, its contribution suffers from its low coverage at the considered conditions. These results are in good agreement with the experimental results.