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

Direct CO2 hydrogenation into linear alpha-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 beta-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.

Automated summary

This study systematically investigated the interaction between Reverse Water-Gas Shift (RWGS) and Fischer-Tropsch Synthesis (FTS) during CO2 hydrogenation using Na-Fe5C2 catalysts. The study found that Na-Fe5C2 catalysts are enriched with FeOx sites, which facilitate RWGS reaction, but the CO2 conversion is limited by the subsequent FTS step due to a lack of available FeCx sites. The performance of the catalyst is controlled by the properties and relative quantities of the two different active sites.