Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Tsinghua University, Beijing, 100084, China.
Nat Commun. 2018 Apr 23;9(1):1610. doi: 10.1038/s41467-018-03795-8.
The current industrial ammonia synthesis relies on Haber-Bosch process that is initiated by the dissociative mechanism, in which the adsorbed N dissociates directly, and thus is limited by Brønsted-Evans-Polanyi (BEP) relation. Here we propose a new strategy that an anchored Fe cluster on the θ-AlO(010) surface as a heterogeneous catalyst for ammonia synthesis from first-principles theoretical study and microkinetic analysis. We have studied the whole catalytic mechanism for conversion of N to NH on Fe/θ-AlO(010), and find that an associative mechanism, in which the adsorbed N is first hydrogenated to NNH, dominates over the dissociative mechanism, which we attribute to the large spin polarization, low oxidation state of iron, and multi-step redox capability of Fe cluster. The associative mechanism liberates the turnover frequency (TOF) for ammonia production from the limitation due to the BEP relation, and the calculated TOF on Fe/θ-AlO(010) is comparable to Ru B5 site.
当前的工业氨合成依赖于 Haber-Bosch 过程，该过程由离解机制引发，其中吸附的 N 直接离解，因此受到 Brønsted-Evans-Polanyi (BEP) 关系的限制。在这里，我们提出了一种新的策略，即在θ-AlO(010)表面上的锚定 Fe 簇作为氨合成的多相催化剂，通过第一性原理理论研究和微观动力学分析进行研究。我们已经研究了 Fe/θ-AlO(010)上 N 转化为 NH 的整个催化机制，并发现吸附的 N 首先被氢化为 NNH 的缔合机制占主导地位，而不是离解机制，这归因于铁的大自旋极化、低氧化态和 Fe 簇的多步氧化还原能力。缔合机制使氨合成的周转频率 (TOF) 从 BEP 关系的限制中解放出来，并且在 Fe/θ-AlO(010)上计算的 TOF 可与 Ru B5 位相媲美。
