Heterogeneous Fe<sub>3</sub> single-cluster catalyst for ammonia synthesis via an associative mechanism.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 29686395.
- Also identified by DOI 10.1038/s41467-018-03795-8 and PMC identifier 5913218.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The current industrial ammonia synthesis relies on Haber-Bosch process that is initiated by the dissociative mechanism, in which the adsorbed N<sub>2</sub> dissociates directly, and thus is limited by Brønsted-Evans-Polanyi (BEP) relation. Here we propose a new strategy that an anchored Fe<sub>3</sub> cluster on the θ-Al<sub>2</sub>O<sub>3</sub>(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<sub>2</sub> to NH<sub>3</sub> on Fe<sub>3</sub>/θ-Al<sub>2</sub>O<sub>3</sub>(010), and find that an associative mechanism, in which the adsorbed N<sub>2</sub> 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<sub>3</sub> 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<sub>3</sub>/θ-Al<sub>2</sub>O<sub>3</sub>(010) is comparable to Ru B5 site.