Effect of Metal Dispersion in Rh-Based Zeolite and SiO2 Catalysts on the Hydroformylation of Olefin Mixtures from Fischer–Tropsch Synthesis

This study investigates the hydroformylation of C5+ olefins derived from Fischer–Tropsch synthesis (FTS) using Rh-based catalysts supported on zeolites (MFI, MEL) and SiO2. A series of catalysts were synthesized through two different methods: a one-pot hydrothermal crystallization process, which results in highly dispersed Rh species encapsulated within the zeolite framework (Rh@MFI, Rh@MEL), and an impregnation method that produces larger Rh nanoparticles exposed on the support surface (Rh/MFI, Rh/MEL, Rh/SiO2). Characterization techniques such as BET, TEM, and FTIR were employed to evaluate different catalysts, revealing significant differences in the dispersion and accessibility of Rh species. Owing to its more accessible mesoporous structure, Rh/SiO2 with a pore size of 5.6 nm exhibited the highest olefin conversion rate (>90%) and 40% selectivity to C6+ aldehydes. In contrast, zeolite-encapsulated catalysts exhibited higher selectivity for C6+ aldehydes (~50%) due to better confinement and linear aldehyde formation. This study also examined the influence of FTS byproducts, including paraffins and short-chain olefins, on the hydroformylation reaction. Results showed that long-chain paraffins had a negligible effect on olefin conversion, while the presence of short-chain olefins, such as propene, reduced both olefin conversion and aldehyde selectivity due to competitive adsorption. This work highlights the critical role of catalyst design, olefin diffusion, and feedstock composition in optimizing hydroformylation performance, offering insights for improving the efficiency of syngas-to-olefins and aldehydes processes.