Cilpa-Karhu Geraldine, Laasonen Kari
Department of Chemistry and Materials Science, Aalto University, COMP centre of Excellence in computational Nanoscience, FI-OOO76 Aalto, Finland.
Phys Chem Chem Phys. 2018 Jan 24;20(4):2741-2753. doi: 10.1039/c7cp06473j.
Single-shell carbon-encapsulated iron nanoparticles (SCEINs), Fe@C, have been shown to be charge-transfer complexes that can act as effective catalysts in the hydrogen and oxygen evolution reactions. A new generation of Fe-based catalysts for Fischer-Tropsch synthesis (FTS) which resembles SCEINs, e.g. single carbide nanoparticles encapsulated in carbon shells, has demonstrated enhanced activity and stability for FTS as compared to other carbon-supported Fe-based FTS. Thus the catalytic ability of SCEINs for the water splitting reactions and the Fe-based FTS catalyst with SCEINs-like features stimulated our exploration of SCEINs-catalyzed FTS. We performed ab initio DFT calculations using a realistic SCEINs model system Fe55@C240 to investigate for the first time the adsorption of the main reactants in FTS (CO and H/H2) and further to evaluate the catalytic ability of Fe55@C240 by reproducing the key steps of the well-known Fe-based FTS mechanisms (carbide, enol and CO insertion). Our calculations revealed: (i) a determinant role of Fe in enhancing CO adsorption (ii) strong cooperative effects with the adsorbates that stabilize the binding (iii) a less favourable two-sites reaction on Fe55@C240 due to preferential positions of the reactants farther to each other which prevent enol and carbide FTS mechanisms. We propose therefore a possible CO insertion path for hydrocarbon growth on Fe55@C240.
单壳碳包覆铁纳米颗粒（SCEINs，即Fe@C）已被证明是电荷转移络合物，可作为析氢和析氧反应的有效催化剂。新一代用于费托合成（FTS）的铁基催化剂类似于SCEINs，例如碳壳包裹的单碳化物纳米颗粒，与其他碳负载铁基FTS催化剂相比，已证明其对FTS具有更高的活性和稳定性。因此，SCEINs对水分解反应的催化能力以及具有SCEINs类似特征的铁基FTS催化剂激发了我们对SCEINs催化FTS的探索。我们使用实际的SCEINs模型系统Fe55@C240进行了从头算DFT计算，首次研究了FTS中主要反应物（CO和H/H2）的吸附，并通过重现著名的铁基FTS机制（碳化物、烯醇和CO插入）的关键步骤进一步评估了Fe55@C240的催化能力。我们的计算结果表明：（i）Fe在增强CO吸附方面起决定性作用；（ii）与吸附质有强烈的协同效应，使结合稳定；（iii）由于反应物彼此距离较远的优先位置，Fe55@C240上不太利于双位点反应，这阻碍了烯醇和碳化物FTS机制。因此，我们提出了一种在Fe55@C240上烃生长的可能的CO插入路径。
