Design of Iron-Based Fischer–Tropsch Synthesis Catalysts for Directly Converting Syngas to Value-Added Chemicals and Clean Fuels

Abstract

Conspectus Fischer–Tropsch synthesis (FTS) represents a key technology for converting syngas into fuels and value-added chemicals. Despite decades of industrial application, it remains constrained by three persistent challenges: the dynamic reconstruction of active phases under working conditions, broad hydrocarbon distributions arising from complex reaction pathways, and substantial CO2 formation via the water–gas shift (WGS) side reaction. To address these challenges, our group has made continuous efforts through three stages in the last dozen years: establishing the relationship between active-phase dynamics and catalytic performance, regulating product distribution through electronic modulation and dual-site coupling, and suppressing WGS activity by engineering hydrophobic microenvironments. Relating active-phase dynamics to catalytic performance requires resolving the formation and transformation of Fe phases during FTS. Iron oxide precursors undergo reduction and carburization to form iron carbides, which serve as key active phases for CO activation, C–C coupling, and hydrocarbon formation. Analysis of the reduction and carburization pathways of Fe species, together with the evolution of surface carbon species, allowed us to correlate bulk and surface Fe-phase compositions with catalytic performance. These results provide a mechanistic basis for controlling iron carbide formation under working conditions. Building upon this understanding of active-phase dynamics, we explored strategies to direct reaction pathways and product distributions. Electronic modulation of Fe-based catalysts modified the electronic environment of iron carbide phases and, consequently, product selectivity. Spatially organized multifunctional active sites, in turn, enabled the sequential transformation of reaction intermediates through tandem catalysis. The resulting design framework links active-phase regulation with coordinated control of catalytic functions, reaction pathways, and product distribution. A key insight emerging from our studies is that reaction-generated H2O is not merely a reaction by-product but an important catalytic variable influencing active-phase stability and reaction pathways. Under FTS conditions, H2O can interact with iron carbide phases and induce oxidation to Fe3O4, resulting in enhanced WGS activity and CO2 formation. This understanding motivated the development of hydrophobic microenvironment engineering to regulate the local behavior of H2O, including its adsorption, migration, and residence time near active phases. By constructing hydrophobic interfaces and tailored porous architectures, we effectively regulated the local interaction between H2O and iron carbide phases, thereby suppressing iron carbide oxidation and the WGS side reaction while maintaining efficient transport of reactants and products. These studies trace a progression from understanding active-phase dynamics to controlling reaction pathways and, ultimately, regulating the local behavior of reaction-generated H2O within hydrophobic microenvironments. This framework links active-phase stability, intermediate transformation, molecular transport, and carbon efficiency and may also inform the design of catalytic systems in which in situ-generated molecules alter active-site structures and competing reaction pathways.