Shielding the Hägg carbide by a graphene layer for ultrahigh carbon efficiency during syngas conversion.

Abstract

Fischer-Tropsch synthesis represents a key endeavor aimed at converting nonpetroleum carbon resources into clean fuels and valuable chemicals. However, the current state-of-the-art industrial FTS employing Fe-based catalysts is still challenged by the low carbon efficiency (<50%), mainly attributed to the prominent formation of CO₂ and CH₄ resulting from the nonregulated side water gas shift reaction. Herein, we describe a shielding strategy involving the encapsulation of the active Hägg carbide (χ-Fe₅C₂) by a graphene layer, exhibiting excellent resilience under reaction conditions and exposure to air, thereby eliminating the need for reduction or activation before the Fischer-Tropsch synthesis reaction. The graphene layer helps to stabilize the Hägg carbide active phase, and more importantly, greatly suppresses the side water gas shift reaction. Theoretical calculations suggest that graphene shielding inhibits the water gas shift reaction by reducing the absorption strength of OH_x species. Remarkably, the optimum χ-Fe₅C₂@Graphene catalyst demonstrates a minimized CO₂ and CH₄ formation of only 4.6% and 5.9%, resulting in a high carbon efficiency (ca. 90%) for value-added products. These results are expected to inspire unique designs of Fe-based nanocomposite for highly efficient FTS with regulated carbon transfer pathways.