Insight into the detailed mechanism of the Sabatier reaction on iron is essential for the design of cheap, environmentally benign, efficient and selective catalytic surfaces for CO₂ reduction. Earlier attempts to unravel the mechanism of CO₂ reduction on pure metals including inexpensive metals focused on Ni and Cu; however, the detailed mechanism of CO₂ reduction on iron is not yet known. We have, thus, explored with spin-polarized density functional theory calculations the relative stabilities of intermediates and kinetic barriers associated with methanation of CO₂ via the CO and non-CO pathways on the Fe (111) surface. Through the non-CO (formate) pathway, a dihydride CO₂ species (H₂CO₂), which decomposes to aldehyde (CHO), is further hydrogenated into methoxy, methanol and then methane. Through the CO pathway, it is observed that the CO species formed from dihydroxycarbene is not favorably decomposed into carbide (both thermodynamically and kinetically challenging) but CO undergoes associative hydrogenation to form CH₂OH which decomposes into CH₂, leading to methane formation. Our results show that the transformation of CO₂ to methane proceeds via the CO pathway, since the barriers leading to alkoxy transformation into methane are high via the non-CO pathway. Methanol formation is more favored via the non-CO pathway. Iron (111) shows selectivity towards CO methanation over CO₂ methanation due to differences in the rate-determining steps, i.e., 91.6 kJ mol⁻¹ and 146.2 kJ mol⁻¹, respectively.

中文翻译：

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DFT研究Fe（111）上CO 2和CO甲烷化的机理

深入了解Sabatier对铁的反应的详细机理对于设计廉价，对环境无害，高效且选择性的CO ₂还原催化表面至关重要。早期尝试揭示纯金属（包括以镍和铜为重点的廉价金属）上的CO ₂还原机理的尝试；但是，还不清楚CO ₂还原铁的详细机理。因此，我们已经利用自旋极化密度泛函理论探索了通过Fe（111）表面上的CO和非CO途径与CO ₂甲烷化相关的中间体和动力学势垒的相对稳定性。通过非CO（甲酸酯）途径，产生了二氢CO ₂物种（H ₂分解为醛（CHO）的CO ₂）被进一步氢化为甲氧基，甲醇，然后为甲烷。通过CO途径，观察到由二羟基卡宾形成的CO物种不会被有利地分解为碳化物（在热力学和动力学上都具有挑战性），但是CO经历缔合加氢形成CH ₂ OH分解为CH ₂导致甲烷的形成。我们的结果表明，由于通过非CO途径导致烷氧基转化为甲烷的障碍很高，因此CO ₂转化为甲烷是通过CO途径进行的。通过非CO途径更有利于形成甲醇。铁（111）相对于CO ₂表现出对CO甲烷化的选择性由于速率确定步骤中的差异（即分别为91.6 kJ mol ^-1和146.2 kJ mol ^-1）而导致甲烷化。