Iron catalysts with homogenous phase composition have shown a reduced tendency to form CO₂. Using this information as a design principle, the team developed an effective way to synthesize a catalyst with pure χ-Fe₅C₂ phase by passivating Raney iron — via exposition to 1% oxygen in He at room temperature for 20 h — followed by a carburization step with a hydrogen-rich syngas mixture at 350 °C. Further modification with manganese, which is known to boost reactivity and control the selectivity in FT synthesis, resulted in a catalyst characterized by excellent catalyst-time-yield (CTY) and LAO selectivity under industrially relevant reaction conditions (pictured). Remarkably, the selectivity to CO₂ remains low (below 10%) at 250 °C and only increases moderately at higher temperatures. Structural analysis confirmed the stability of the pure χ-Fe₅C₂ phase over prolonged reaction time. Such phase stability appears to be quite important; in fact, the generation of different phases such as iron oxides — which are good catalysts for the water–gas shift reaction — would result in the formation of CO₂ from CO and water, reducing the overall selectivity. Theoretical calculations helped to rationalize the cause of the low CO₂ selectivity and show how for χ-Fe₅C₂, the energy barrier related to H₂O formation is lower compared to CO₂ formation. Therefore, upon CO dissociation oxygen is preferentially removed as water.

Whether this catalyst can be easily used for practical applications remains an open question at this stage. However, the achievements of this phase-pure χ-Fe₅C₂ catalyst represent an important step towards the development of FT schemes for the preparation of LAOs.

具有均相组成的铁催化剂形成 CO₂ 的趋势降低。利用这些信息作为设计原则，该团队开发了一种有效的方法，通过钝化雷尼铁合成具有纯 χ-Fe₅C₂ 相的催化剂——在室温下暴露于 1% 的 He 中 20 小时——然后在 350 °C 下使用富氢合成气混合物进行渗碳步骤。 众所周知，锰可以提高 FT 合成中的反应性并控制选择性，用锰进一步改性，从而得到一种催化剂，其特点是在工业相关反应条件下具有优异的催化剂时间产率 （CTY） 和 LAO 选择性（如图）。值得注意的是，在 250 °C 时，对 CO₂ 的选择性仍然很低（低于 10%），并且在较高温度下仅适度增加。结构分析证实了纯 χ-Fe₅C₂ 固定相在较长反应时间内的稳定性。这种相稳定性似乎非常重要;事实上，产生不同的相，如氧化铁——它们是水-气变换反应的良好催化剂——会导致 CO 和水形成 CO₂，从而降低整体选择性。理论计算有助于合理化 CO₂ 选择性低的原因，并表明 χ-Fe₅C₂ 与 CO₂ 形成相比，与 H₂O 形成相关的能垒更低。因此，在 CO 解离时，氧优先以水的形式去除。

这种催化剂是否能轻松用于实际应用，在现阶段仍是一个悬而未决的问题。然而，这种相纯 χ-Fe₅C₂ 催化剂的成就代表了朝着开发制备 LAO 的 FT 方案迈出的重要一步。