Fischer-Tropsch (FT) synthesis represents one of the most advanced technologies to convert fossil and renewable carbon feedstock into liquid fuels. The technology is well established for the conversion of synthesis gas derived from natural gas. Currently, significant efforts are underway to realize coal-to-liquids (CTL) processes in certain parts of the world where coal is a cheap and abundant resource. Compared to natural-gas based FT, CTL processes face an important challenge: since the H/C ratio of coal is too low, the process requires the water-gas shift (WGS) reaction to increase the H2/CO ratio of the FT feedstock. This leads to significant CO2 emissions. In essence, this leads to the requirement to couple CTL processes to CO2 capture. Typically, conventional Fe-based FT catalyst converts 30% of feeding CO into by-products CO2 in FT units. Taking into account the whole CTL process, decreasing CO2 release in FT unit will dramatically reduce the pilot costs and enhance productivity. To overcome this challenge, we present a completely novel and scalable preparation method of stable and phase-pure ε(')-iron carbide Fischer-Tropsch catalysts with a near-zero intrinsic (primary) CO2 selectivity. In situ characterization techniques are employed to clarify the formation and phase composition of ε(’)-carbide and the catalytic performance of these novel catalysts was evaluated under industrial FT conditions. Importantly, no catalyst deactivation was observed and the ε(’)-carbide phase was intrinsically stable under these conditions, even after a high temperature excursion. This is contrary to current belief that ε(’)-carbide is not stable under industrial FT conditions. These results shed a completely new view on the utility of ε(’)-carbide, which has hitherto been disregarded in favor of Hägg carbide as the stable and catalytically active phase. We unequivocally show that ε(’)-carbide can convert syngas to liquid fuels without CO2 as a primary product. Thus, we achieved to prepare a catalyst with low CO2-selectivity.

Novel epsilon-iron carbide Fischer-Tropsch catalysts with stable and low-CO2 selectivity

2019 Spring National Meeting

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