Ammonium-exchange tuning of hierarchical Co/Beta catalysts for jet fuel-range hydrocarbons via fischer-tropsch hydrocracking

The integration of Fischer-Tropsch synthesis (FTS) and hydrocracking over bifunctional catalysts offers a sustainable route for converting syngas into middle-distillate hydrocarbons, particularly jet fuel-range products (C 8 -C 16 ). In this work, Co/Beta zeolite catalysts were designed as bifunctional catalysts for integrated Fischer-Tropsch synthesis and hydrocracking. A sequential post-synthetic modification strategy, consisting of NaOH desilication followed by controlled NH4 + ion exchange, was applied to introduce mesoporosity and subsequently tune acidity in Beta zeolites. This approach enables acidity regulation within a largely preserved hierarchical pore structure, allowing the respective roles of textural properties and acid-site distribution in bifunctional Fischer-Tropsch and hydrocracking performance to be evaluated. Comprehensive physicochemical characterization reveals that intermediate NH 4 + exchange (1.0 M) promotes an optimal balance between mesoporosity (∼40%, average pore diameter ∼ 19 nm), acidity, and moderated cobalt-support interaction. Quantitative analysis shows that this balance governs hydrocarbon chain growth. Under FTS conditions (235 °C, 20 bar, H 2 /CO = 2), the optimized Co/H-meso Beta catalyst achieves ∼ 70% CO conversion and ∼ 50% selectivity toward C 8 –C 16 hydrocarbons. Correlation analysis demonstrates that jet fuel selectivity is strongly dependent on the combined effect of mesoporosity, acid site distribution, and reducibility, rather than mesoporosity alone. These findings demonstrate that controlled post-synthetic acidity regulation of Beta zeolite is critical for directing product selectivity in bifunctional FTS catalysts. They provide insight into the structure-performance relationships governing single-step jet fuel synthesis from syngas.