Synergistic effect of K and Zn on Fe-based catalysts for efficient CO2 hydrogenation

Abstract

Excessive emission of CO₂ into the atmosphere has severely impacted the global ecological environment. Converting CO₂ into valuable chemicals and fuels is of great significance for sustainable development. However, low activity and undesirable selectivity often result from the inherent inertness of CO₂. Herein, K- or/and Zn-modified Fe-based catalysts were prepared by an incipient-wetness impregnation method for CO₂ hydrogenation via a cascade reaction. The results indicate that K species exist as K₂O while Zn species exist as ZnFe₂O₄. In the CO₂ hydrogenation pathway, K₂O facilitates the adsorption of CO₂ and restrains the adsorption of H₂, accelerating the transformation of CO₂ into C₂–C₄ olefins rather than paraffins while Zn species promote the dispersion of Fe species, leading to improved activity. Synergistically, a K- and Zn-modified Fe-based catalyst (2Zn–10K–Fe/Al) shows excellent catalytic CO₂ hydrogenation activity, achieving a CO₂ conversion of 77% which is 1.8 times that (42%) of the unmodified Fe-based catalyst (Fe/Al). Our catalyst also shows a significantly promoted selectivity to C₂–C₄ olefins of 17% in comparison with the Fe/Al catalyst (0%). It is envisioned that such a binary effect of elements might contribute to the low-cost and industrial production of Fe-based catalysts for selective CO₂ conversion.