Selective fabrication of χ-Fe5C2 by interfering surface reactions as a highly efficient and stable Fischer-Tropsch synthesis catalyst

Abstract

Fabrication of χ-Fe5C2 active phase is important for efficient iron-based Fischer-Tropsch synthesis but faces a challenge in the controllable synthesis of high purity phase. Herein, we report selective synthesis of χ-Fe5C2 catalysts by interfering surface reactions during thermal treatment. In-situ analyses provided insight into the mechanism of the structure evolution of iron-based catalysts under varied thermal treatment atmospheres and conditions. The atmosphere of 64 %H2/32 %CO/4 %Ar yields a compromise among the competitive oxygen removal, carbon permeation, hydrogenation and carbon deposition reactions, thus selectively forming high-purity χ-Fe5C2. Such catalyst shows high CO conversion of 96 %, selectivity to C5+ hydrocarbons of 40 % and light olefins of 30 %, and good stability under mild conditions (250 °C, 2.0 MPa). A plausible catalyst structure-performance relation is finally established by combining kinetics analysis with multiple characterization techniques. The simultaneously enhanced activity and selectivity are related to the more terrace sites of χ-Fe5C2, and the pre-formed carbon coating during pretreatment process improves catalyst stability.