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

• Published in: Angewandte Chemie International Edition Vol. 61; no. 22; pp. e202116517 - n/a
• Main Authors: Yang, Qingxin, Kondratenko, Vita A., Petrov, Sergey A., Doronkin, Dmitry E., Saraçi, Erisa, Lund, Henrik, Arinchtein, Aleks, Kraehnert, Ralph, Skrypnik, Andrey S., Matvienko, Alexander A., Kondratenko, Evgenii V.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 23.05.2022; John Wiley and Sons Inc
• Edition: International ed. in English
• Subjects: Alkali metals; Carbon dioxide; Catalysts; CO2 Utilization; Electronegativity; Heavy metals; Heterogeneous Catalysis; Hydrogenation; Iron; Iron carbides; Kinetics; Promoters; Rate constants
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202116517

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. Iron carbides (FeCx) presence in Fe‐based catalysts does not secure efficient CO2 hydrogenation to C2+‐hydrocarbons. The efficiency depends on the ability of FeCx to activate CO, CO2 and H2. The kinetics of these processes is affected by perturbation of electronic properties of Fe in FeCx by an alkali metal (Li, Na, K, Rb or Cs) promoter. This knowledge can be valued for the design of catalysts for other reactions where such promoters are used.