Light olefin synthesis from CO₂ hydrogenation over K-promoted Fe-Co bimetallic catalysts

This work investigates the effects of potassium addition on light olefin production from CO₂ hydrogenation over the Al₂O₃-supported Fe-Co bimetallic catalysts. The addition of small amount of K on the Fe-Co catalyst significantly enhanced C₂-C₄ olefin formation. The C₂-C₄ olefins predominated among C₂⁺ hydrocarbons at K/Fe atomic ratio of 1. Temperature-programmed desorption experiments demonstrated that K addition diminished the weakly adsorbed hydrogen but enhanced CO₂ adsorption on the catalyst surface, which led to significantly enhanced production of light olefins. For C₂-C₄ olefin synthesis at 573 K and 1.0 MPa, the K-promoted Fe-Co/Al₂O₃ catalyst also showed better performance than the K-promoted Fe-Mn/Al₂O₃ catalyst which is known as a good catalyst for olefin production, under the present conditions employed. The pathway of olefin formation from CO₂ hydrogenation was analyzed. Light olefins were formed via two-step reactions over K-promoted Fe-Co catalysts with the formation of CO or CO-like intermediate as the first step. Some of these olefins could be further hydrogenated to paraffins, depending on the type and concentration of chemisorbed hydrogen on the catalyst surface.