Potassium as a Versatile Promoter to Tailor the Distribution of the Olefins in CO2 Hydrogenation over Iron‐Based Catalyst

Abstract

AbstractThe effect of K on the distribution and productivity of the olefins in CO2 hydrogenation over the single‐walled carbon nanotubes (SWNTs) supported Fe catalysts was systematically investigated. The promotion of K not only effectively suppressed the formation of the undesired light paraffins (CH4 and C20−C40), but also significantly affected the distribution and the productivity of the olefins. The highest selectivity and productivity of light olefins (C2=−C4=) of 27 % and 16 μmolCO2 gFe−1 s−1, respectively, were obtained at 7 wt% of K, while the highest selectivity and productivity of heavy olefins (C5+=) of 40 % and 27 μmolCO2 gFe−1 s−1, respectively, were obtained at 3 wt% of K under the same reaction conditions. At 3 wt% of K and above, the overall selectivity to the olefins (inclusive of light olefins and heavy olefins) remained at as high as ca. 60 % at high CO2 conversion of ca. 50 %. Comprehensive characterizations revealed that the K promoter enhanced the basicity of the catalyst, which facilitates the formation of χ‐Fe5C2, the key active phase for CO2 hydrogenation. A good linear relationship is established between the surface basicity and the content of χ‐Fe5C2. Moreover, the K promoter weakened the adsorption of the olefins, which inhibited the secondary hydrogenation of the olefins, thus improving the selectivity to the olefins. This work demonstrates that K is a highly promising promoter for the tailoring of the types of the olefinic products in CO2 hydrogenation.