Role of SiC Nanoparticles in Promoting the Activity and Selectivity of the Co/Al ₂ O ₃ @Al Catalyst for Fischer–Tropsch Synthesis

The SiC NP-modified high thermal conductivity Co/Al 2 O 3 @Al Fischer–Tropsch synthesis (FTS) catalyst has been proven to significantly enhance catalytic activity and selectivity toward long-chain hydrocarbons (C 5+ ), but the underlying mechanism responsible for this promotional effect remains unclear. In this study, commercially available SiO 2 NPs are used as a substitute for SiC NPs to prepare a cost-effective SiO 2 -modified Co/Al 2 O 3 @Al catalyst (Co/AS-O) for improved FTS performance, serving as a reference to elucidate the unique role of SiC NPs in enhancing FTS performance. Systematic characterizations demonstrate that SiC promotes the formation of the hexagonal close-packed (HCP) Co phase, yielding a higher intrinsic activity. In contrast, the face-centered cubic (FCC) Co phase predominates in the Co/AS-O and an unmodified reference catalyst (Co/A-Y). Although both modified catalysts exhibit enhanced CO conversion, the superior activity of the SiC NP-modified catalyst (Co/AS-C) stems from an increased density of active sites and its higher intrinsic activity, as evidenced by a higher turnover frequency (TOF). In contrast, the enhancement for Co/AS-O is solely due to a greater number of exposed Co 0 sites. Moreover, the incorporation of NPs enhances *CO adsorption and restricts the activity of surface *H species, collectively establishing a *C-rich microenvironment that promotes chain growth and olefin formation. This study provides a fundamental understanding of how inert NPs modulate the FTS performance of the thermally conductive Co/Al 2 O 3 @Al catalyst.