The Conversion of Syngas to Long-Chain α-Olefins over Rh-Promoted CoMnOx Catalyst

The direct synthesis of long-chain α-olefins from syngas offers a strategically vital pathway for producing high-value chemicals from alternative carbon resources. However, achieving high selectivity toward C5+ olefins remains challenging due to competing paraffin formation and difficulties in precisely regulating chain growth kinetics. To mitigate these critical challenges, a series of Rh-promoted Co-Mn catalysts supported on SiO2 were synthesized using a carbon-mediated impregnation strategy for the direct conversion of syngas to long-chain α-olefins (C5+). The introduction of Rh significantly enhanced both catalytic activity and C5+ olefin selectivity. The optimal 1.1 wt% Rh-loaded catalyst achieved 24.6% CO conversion and 46.0% total olefin selectivity, with 34.2% of the selectivity toward C5+ olefins, while maintaining low CH4 (6.2%) and CO2 (<1%) selectivity. Comprehensive characterization techniques, including XRD, H2-TPR, XPS, and TEM/HAADF-STEM, revealed that the carbon-mediated method facilitated the formation of highly dispersed Co3O4 nanoparticles with abundant oxygen vacancies and strengthened the Co-MnOx interface. Rh promotion modulated the cobalt speciation (Co0/Co2+), improved reducibility, and enhanced the metal-support interaction. This promoted chain growth and olefin desorption while suppressing over-hydrogenation. This study demonstrates the efficacy of Rh promotion and carbon mediation in designing high-performance Fischer-Tropsch catalysts for selective α-olefin synthesis, offering new insights into the design of efficient metal-oxide interfacial catalysts.