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

Abstract

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.