Surface Si decoration of ultrafine NaFeMn-Si catalyst enabling high Fe-phase electron density for effectively converting syngas to aromatics

Abstract

• Preparing NaFeMn-Si catalyst with ultrafine crystals through Si modification. • Improving Fe phase electron density by decoration of Na 2 SiO 3 on crystal surface. • Promoting olefin to paraffin ratio to reduce by-product via high electron density. • Achieving 90% conversion with 64% aromatic selectivity under optimal condition. Effectively converting syngas to aromatics attracts widespread attention for its potential value in alleviating the scarcity of oil resources, while the promising catalysts composited with Fe-based oxides and zeolites are typically plagued by lower aromatics selectivity. Herein, ultrafine NaFeMn-Si catalyst is designed via the surface decoration of SiO 2 -Na 2 SiO 3 on the crystal surface by a unique post-modification strategy. Experiments and calculations demonstrate that surface decoration of Si reduces the NaFeMn-Si crystal size to 6.7 nm by potently preventing agglomeration, which greatly enlarges the active surface area to promote the catalytic activity. Moreover, the in situ formed surface Na 2 SiO 3 , which is converted from Na 2 O under the synergism between Si and Na species, remarkably weakens binding force of –SiO 3 in comparison with –O bond. Thereby, the electron delocalization of Na is enhanced by releasing the outer electron to Fe, significantly increasing the electron density of Fe phase. This elaborate modification strategy effectively modulates the adsorption and dissociation of H 2 and CO molecules, which facilitates the formation of iron carbide as the active center, not only improving the intermediary olefin/paraffin ratio to achieve a superior catalytic performance of 64% aromatic selectivity with 90% CO conversion, but also providing an appealing and instructive design guidance for the aromatics synthesis over Fe-based composite catalysts.