Understanding kinetically interplaying reverse water-gas shift and Fischer-Tropsch synthesis during CO2 hydrogenation over Fe-based catalysts

• Published in: Applied catalysis. A, General General, 2022-07, Vol.641, p.118682, Article 118682
• Main Authors: Xu, Minjie, Cao, Chenxi, Xu, Jing
• Format: Article
• Language: English
• Subjects: Active sites; Alkali metal; Alkenes; Carbon dioxide; Catalysts; Chemical synthesis; CO2 hydrogenation; Conversion; Fischer-Tropsch process; Hydrogenation; Intrinsic kinetics; Iron-based catalyst
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2022.118682

Direct CO2 hydrogenation into linear α-olefins presents a promising route in carbon-neutral chemical manufacture. This work systematically investigated the variable interplay between Reverse Water-Gas Shift (RWGS) and Fischer-Tropsch Synthesis (FTS) during CO2 hydrogenation using model Na-Fe5C2 catalysts, combining dynamic/steady-state CO/CO2 hydrogenation performance, intrinsic kinetics and multiple characterization results. Na-Fe5C2 proves to be surface-enriched with FeOx sites over which RWGS readily proceeds. Meanwhile, CO2 conversion under integral reaction conditions is limited by the subsequent FTS step due to a lack of available FeCx sites. The catalyst performance is steered by the properties and relative quantities of the two different active sites. Na addition promotes the refresh of FeOx sites and β-elimination of alkyl intermediates over FeCx sites, but at the cost of inhibiting the surface fraction of FeCx sites and thus the single-pass CO2 conversion. These fundamental understandings will enlighten further development of CO2 hydrogenation catalysts with improved hydrocarbon yields. [Display omitted] •Kinetically interplaying RWGS and FTS kinetics in CO2 hydrogenation elaborated.•CO2 conversion improved/inhibited under differential/integral conditions by Na.•Coupling between RWGS and FTS tuned by surface fractions of different active sites.•FeOx proved dominant on bulk χ-Fe5C2 model catalyst surface.•Supply of surface FeCx sites on catalyst surface limiting CO2 conversion rates.