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

Abstract

Abstract The effect of K on the distribution and productivity of the olefins in CO 2 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 (CH 4 and C 2 0 −C 4 0 ), but also significantly affected the distribution and the productivity of the olefins. The highest selectivity and productivity of light olefins (C 2 = −C 4 = ) of 27 % and 16 μmol CO2 g Fe −1 s −1 , respectively, were obtained at 7 wt% of K, while the highest selectivity and productivity of heavy olefins (C 5+ = ) of 40 % and 27 μmol CO2 g Fe −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 CO 2 conversion of ca . 50 %. Comprehensive characterizations revealed that the K promoter enhanced the basicity of the catalyst, which facilitates the formation of χ ‐Fe 5 C 2 , the key active phase for CO 2 hydrogenation. A good linear relationship is established between the surface basicity and the content of χ ‐Fe 5 C 2 . 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 CO 2 hydrogenation.