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

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 SiO₂-Na₂SiO₃ 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 Na₂SiO₃, which is converted from Na₂O under the synergism between Si and Na species, remarkably weakens binding force of –SiO₃ 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 H₂ 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.