Identifying Performance Descriptors in CO₂ Hydrogenation over Iron-Based Catalysts Promoted with Alkali Metals

Alkali metal promoters have been widely employed for preparation of heterogeneous catalysts used in many industrially important reactions. However, the fundamentals of their effects are usually difficult to access. Herein, we unravel mechanistic and kinetic aspects of the role of alkali metals in CO₂ hydrogenation over Fe-based catalysts through state-of-the-art characterization techniques, spatially resolved steady-state and transient kinetic analyses. The promoters affect electronic properties of iron in iron carbides. These carbide characteristics determine catalyst ability to activate H₂ , CO and CO₂ . The Allen scale electronegativity of alkali metal promoter was successfully correlated with the rates of CO₂ hydrogenation to higher hydrocarbons and CH₄ as well as with the rate constants of individual steps of CO or CO₂ activation. The derived knowledge can be valuable for designing and preparing catalysts applied in other reactions where such promoters are also used.