The conversion of greenhouse gases, such as CO₂ and CH₄, to value chemicals is a major challenge, because of the high stability of both molecules. In this study, density functional theory (DFT) calculations with long-range corrections and ONIOM were used to analyze the reaction mechanism for the conversion of CO₂ and CH₄ to acetic acid with MFI zeolite exchanged with Be, Co, Cu, Mg, Mn, and Zn cations. Our results demonstrate that (a) the highest reaction barrier on the reaction mechanism is CH₄ dissociation, and the transition state energy in that step is directly related to the energy of the lowest unoccupied molecular orbital and the electronegativity of the metal exchanged zeolites; (b) a charge transfer between CH₄ and the metal cation occurs simultaneously to CH₄ dissociation; (c) CO₂ insertion has a low energy barrier, and the protonation of the acetate species is spontaneous; (d) dispersion interactions are the main contributions to CH₄ adsorption energies, whereas, in the rest of the steps of the reaction mechanism, the contribution of dispersion to the energies of reaction is almost negligible; (e) desorption of acetic acid could be promoted by the coadsorption of water; and (f) CH₄ dissociation on Cu-MFI has an apparent activation energy of 11.5 kcal/mol, and a forward rate constant of 1.1 s^–1 at 398 K.

中文翻译：

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密度泛函理论（DFT）研究揭示了M-交换的MFI（M = Be，Co，Cu，Mg，Mn，Zn）的甲烷和二氧化碳转化为乙酸的催化性能

由于两个分子的高稳定性，将诸如CO ₂和CH _4之类的温室气体转化为有价值的化学物质是一个重大挑战。在这项研究中，使用具有远距离校正的密度泛函理论（DFT）计算和ONIOM分析了MFI沸石与Be，Co，Cu，Mg交换后，CO ₂和CH ₄转化为乙酸的反应机理。Mn和Zn阳离子。我们的结果表明（a）反应机理中最高的反应障碍是CH ₄离解，并且该步骤中的过渡态能量与最低未占据分子轨道的能量和金属交换沸石的电负性直接相关。（b）CH ₄和金属阳离子之间的电荷转移与CH ₄离解同时发生；（c）插入CO _2的能垒低，并且乙酸盐物质的质子化是自发的；（d）分散相互作用是对CH ₄吸附能的主要贡献，而在反应机理的其余步骤中，分散对反应能的贡献几乎可以忽略不计；（e）水的共吸附可促进乙酸的解吸；和（f）CH ₄Cu-MFI上的解离具有11.5 kcal / mol的表观活化能，在398 K下的正向速率常数为1.1 s ^–1。