Activated carbon templated synthesis of hierarchical zeolite Y-encapsulated iron catalysts for enhanced gasoline selectivity in CO hydrogenation

Abstract

Fischer–Tropsch synthesis (FTS) remains a technology of the future for the sustainable production of hydrocarbon fuels. To date, controlling the hydrocarbon selectivity is still a major challenge since the product distribution follows the Anderson–Schulz–Flory (ASF) model, which suggests a maximum gasoline selectivity of ∼48%. In this work, we report the characteristics of zeolite Y-encapsulated iron catalysts whose FTS activity deviates from the ASF model with an enhanced gasoline selectivity of up to 65.7%. The catalysts were synthesized by a low-cost crystallization procedure using activated carbon (AC) as a sacrificial template. The AC template enhanced the dispersion of the Fe nanoparticles and porosity of the catalysts while ensuring effective fixation of the Fe nanoparticles within the zeolite Y crystals. The final catalysts further demonstrated moderate acidity dominated by Lewis acids and a high surface area, with Fe facets which easily convert to high spin Fe₅C₂(510). These properties collaboratively enhanced C–C coupling for direct C_5–11 hydrocarbon synthesis in FTS. The discussions from this work reveal and confirm preliminary relationships that exist between the phases of Fe-based FTS catalysts and their influence on C–C coupling in FTS reactions.