Cobalt-Potassium Synergistic Modification Effects on Fe-Based Catalysts for CO2 Hydrogenation to Low-Carbon Olefins

To enhance the CO₂ hydrogenation activity and low-carbon olefin selectivity of Fe-based catalysts, a strategy involving the use of metal promoters to modulate the structure of active metal centers in catalyst preparation was proposed. The incipient wetness impregnation method was used to introduce modifying agents K and/or Co into the Fe/Al₂O₃ catalyst. Characterization techniques such as XRD, BET, SEM, HRTEM, H₂-TPR, XPS, CO₂-TPD, NH₃-TPD, and TG were employed to investigate the effects of the modifying agents on the dispersion, reducibility, electronic properties, and acid–base properties of active metal species. Furthermore, the influence of K and Co modification on the CO₂ hydrogenation activity and low-carbon olefin selectivity of Fe/Al₂O₃ catalysts was explored. The results revealed that the introduction of K generated more basic sites and electron-rich active metal centers in the catalyst, facilitating the adsorption and activation of CO₂, while suppressing the hydrogenation of olefins and the formation of methane, thus improving the selectivity towards low-carbon olefins. Co promoter facilitated the dispersion of Fe species, exposing more active sites and enhancing the FTS reaction activity, leading to more CO being converted into C₂₊ hydrocarbon products. Under the synergistic effect of K and Co, the CO₂ conversion activity of the Fe-based catalyst significantly increased, achieving a CO₂ conversion rate of 37%, while the selectivity towards C₂-C₄₌ increased to 31.9%.