School of Chemical Engineering, PSU-DUT Joint Center for Energy Research, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P. R. China.
Phys Chem Chem Phys. 2018 May 30;20(21):14694-14707. doi: 10.1039/c8cp02218f.
Catalytic conversion of CO2 including hydrogenation has attracted great attention as a method for chemical fixation of CO2 in combination with other techniques such as CO2 capture and storage. Potassium is a well-known promotor for many industrial catalytic processes such as in Fischer-Tropsch synthesis. In this work, we performed density functional theory (DFT) calculations to investigate the effect of potassium on the adsorption, activation, and dissociation of CO2 over Fe(100), Fe5C2(510) and Fe3O4(111) surfaces. The function of K was analyzed in terms of electronic interactions between co-adsorbed CO2 and K-surfaces which showed conspicuous promotion in the presence of K of the adsorption and activation of CO2. The adsorption strength of CO2 on these surfaces ranks as oct2-Fe3O4(111) > Fe(100) > Fe5C2(510). Generally, we observed a direct proportional correlation between the adsorption strength and the charges on the adsorbates. Adding K on the catalyst surface also reduces the kinetic barrier for CO2 dissociation. CO2 dissociation is more facile to occur on Fe(100) and Fe5C2(510) in the presence of K whereas the Fe3O4(111) surfaces impede CO2 dissociation regardless of the existence of K. Instead, a stable CO3- species is formed upon CO2 adsorption on Fe3O4(111) which will be directly hydrogenated when sufficient H* are available on the surface. Our results highlight the origin of the promotion effect of potassium and provide insight for the future design of K-promoted Fe-based catalysts for CO2 hydrogenation.
二氧化碳的催化转化包括加氢，已作为与 CO2 捕集和封存等其他技术相结合的 CO2 化学固定方法引起了极大的关注。钾是许多工业催化过程（如费托合成）的知名促进剂。在这项工作中，我们进行了密度泛函理论（DFT）计算，以研究钾对 Fe(100)、Fe5C2(510)和 Fe3O4(111)表面上 CO2 的吸附、活化和离解的影响。通过分析共吸附 CO2 和 K-表面之间的电子相互作用来研究 K 的作用，结果表明，在存在 K 的情况下，CO2 的吸附和活化得到了显著促进。这些表面上 CO2 的吸附强度顺序为 oct2-Fe3O4(111) > Fe(100) > Fe5C2(510)。通常，我们观察到吸附强度与吸附物上电荷之间存在直接的正比例关系。在催化剂表面添加 K 还降低了 CO2 离解的动力学障碍。在存在 K 的情况下，CO2 更容易在 Fe(100)和 Fe5C2(510)上离解，而 Fe3O4(111)表面无论是否存在 K 都会阻碍 CO2 离解。相反，在 Fe3O4(111)表面上吸附 CO2 会形成稳定的 CO3-物种，当表面上有足够的 H*时，它将直接被加氢。我们的结果突出了钾的促进作用的起源，并为未来设计用于 CO2 加氢的 K 促进的 Fe 基催化剂提供了深入的见解。
