We present a novel Ce–Fe mixed oxide catalyst promoted with bismuth (Bi), designed to leverage the emerging concept of liquid metal catalysis. Under typical FTS-to-olefins conditions (~350 °C), Bi—melting at 271 °C—exhibits mobility within the solid catalyst matrix. This enables dynamic surface restructuring, enhancing active-site availability and tailoring electronic properties to favor olefin formation.
Catalysts were synthesized via citrate sol-gel and impregnation methods, with Bi and K as promoters. The best-performing formulation, CeBiFe-K, exhibited sixfold increase in CO conversion, eightfold enhancement in olefin yield, and reduced methane selectivity of 17.7% compared to unpromoted Fe catalysts. Characterization (BET, XRD, Raman, FTIR, XPS, TPR/TPD) revealed that Bi promotes catalyst reducibility, generates oxygen vacancies, and facilitates iron-carbide (χ-Fe5C2) formation—key to selective olefin production. Raman and XRD confirmed preferential carbide formation in Bi-promoted catalysts. Additionally, Bi appears to accelerate Fe-oxide reduction and carburization and may serve as a transient oxygen shuttle via redox cycling. This redox activity enhances CO dissociation and oxygen removal (CO→CO2 or H2O), as supported by TPR/TPD profiles. CO-TPD and FTIR indicate weaker CO binding on Bi-modified surfaces, consistent with the promotional effect that facilitates CO activation and chain growth.
This study not only introduces Bi as a novel and effective promoter in Fe-based FTO catalysts but also demonstrates how liquid-like behavior in solid-state systems can be harnessed to achieve tunable catalytic interfaces. These findings offer new insights for the rational design of next-gen catalysts for syngas conversion.