Tuning bifunctional Pt catalysts on Nb, Mo, and W oxide-modified carbon nanofibers for the continuous selective hydrocracking and hydroisomerization of n-hexadecane as a Fischer-Tropsch product model compound

This work investigates bifunctional Pt catalysts supported on carbon nanofibers (CNFs) modified with Nb, Mo, or W oxides for the hydroconversion of n-hexadecane as a model compound of Fischer-Tropsch (FT) products. Oxide functionalization was used to overcome the low intrinsic acidity of carbon supports by introducing proton-donating surface sites while preserving favorable textural properties. The nature of the oxide promoter strongly influenced the metal-acid balance, Pt accessibility, and catalytic behavior. At 350 °C, 20 bar and a WHSV of 7.6 h −1 , Pt supported on bare CNFs showed low activity (18.3% conversion) and a product distribution consistent with a substantial contribution from hydrogenolysis, with 7.9% selectivity to C16 isomers, whereas all oxide-modified catalysts activated hydroisomerization pathways (72.0–82.2% selectivity to C16 isomers). Pt/W-CNF500 exhibited the highest conversion (55.5%) with 85.5% total isomer selectivity and the highest share of multibranched C16 isomers, indicating an effective compromise between acidity and hydrogenation capacity. Reaction temperature mainly controlled conversion and secondary hydrocracking, while space velocity had a limited effect on selectivity. These results demonstrate that oxide-modified CNFs constitute a tunable platform for designing bifunctional catalysts for controlled upgrading of FT-derived products.